Malibu, California (CNN) Two nice ladies building castles in the sand with a cute little girl hardly seems like fodder for the police blotter.

But this is Malibu, where people call the cops on other people just for sitting on the beach. It's been going on for decades. And last weekend, it happened to us.

A private security guard, who said he'd patrolled Escondido Beach for seven years on behalf of homeowners, insisted we were trespassing on private property and threatened us with a $1,500 fine and lifetime beach banishment. Then, when we politely refused to budge, he politely called police.

Two deputies arrived within 20 minutes. It didn't matter that my beach companion works for the California Coastal Commission, or that we carried proof we had a right to be there. (Our papers were in order!)

On Escondido Beach, at least, we were Public Enemy #1. Malibu's Most Unwanted.

It's an old story in California, and particularly in Malibu, where battles over public beach access tend to have no beginning or end, just years and years of middle.

I couldn't believe what I'd heard about how far residents were willing to go to keep the hoi polloi off the sand in front of their multimillion-dollar Malibu beach houses: Padlocked gates, "No Trespassing" signs, "No Parking" signs, boulders and trees blocking access points.

Last summer, for example, a creative property owner in Paradise Cove, the Malibu beach made famous by the 1970s detective show "The Rockford Files," decided to charge surfers $40 for parking and beach access. The Coastal Commission stepped in and stopped the gouging.

We'd heard the stories about rent-a-cops shooing away the unwashed, unwanted masses from the most prized beaches on weekends. I laughed at the time because it seemed like a lot of trouble and expense to keep people away from beaches that are supposed to belong to everyone. I had underestimated the residents' sense of entitlement.

So, yes, I jumped at the opportunity to see if I could get myself kicked off a public beach.

My Coastal Commission friend, Noaki Schwartz, had heard the stories, too. She used to cover the coast for the Associated Press, and we worked together at newspapers in California and Florida. She had just landed a new gig as the Coastal Commission's spokesperson.

Noaki Schwartz, with the California Coastal Commission, watches as the guard returns with two deputies.

As state agencies go, the Coastal Commission is a fun one, overseeing conservation and controlling development of some of the most breathtaking places on the planet. They have say over whether Pebble Beach gets a new golf course, SeaWorld expands, or Santa Barbara can build a new hotel by the sea.

As it nears its 40th year, the commission is stepping up its efforts to make California's coastline accessible to everyone, not just those who can afford to hoard the view.

In early August, reports started coming in about a security guard kicking people off Escondido Beach near Geoffrey's, a popular blufftop restaurant in Malibu's western reaches. Wouldn't it be fun to check it out?

Game on.

Schwartz and I agreed to go undercover, as ourselves. We might be commoners, but we are informed commoners.

For good measure, Schwartz brought along her 6-year-old daughter, Lucia, who loves to build sand castles, tans in an instant, and is thinking she might like it if people called her "Scout" from now on.

The three of us started out at Geoffrey's as ladies who lunch. It was a sublime late summer beach day, all blue sky, white sand and crashing waves. Inland, it was hot as blazes -- 100 degrees or more -- but a cool breeze ruffled the patio umbrellas as we blissfully gazed out at a sparkling, cerulean ocean. We wondered why anyone would want to be anywhere else.

The plan was to hit the beach after polishing off the lobster quiche and crème brulee. Earlier in the summer, a new flight of steps had opened, leading from Geoffrey's deck to the sand below. It wasn't very well marked, but this was the newest Coastal Access entry point.

These are public steps and they lead to a beach, some of which also is public. Not everybody knows this, which is exactly how the residents of Escondido Beach like it.

Escondido means "hidden," after all.

In Oregon and Washington, beaches are public up to the vegetation line. California's beaches belong to everyone, too, but the line is drawn along the mean tide line. That's usually about halfway between where the water is and the line of kelp left on the beach after the last high tide.

In theory, a person could walk along the water for the length of California -- from the Oregon state line to the Mexican border -- without setting foot on private property.

As a practical matter, though, some areas are too rocky, some are underwater, and others have been fenced off by private developers.

To make things simple, California tends to draw the line between public and private this way: Wet sand is public beach, and dry sand is private property.

But that rule of thumb doesn't take into account the myriad easements the Coastal Commission has won since it came into being during the mid-1970s. They did it one permit at a time: Want to build a pool at your beachhouse? Let the public walk across your beach.

Escondido Beach is a patchwork of easements now. Behind one person's house the dry sand may be public, while on either side of the house it isn't. The map looks like Mike Tyson's smile.

But nobody seems to know where the lines are.

Show a security guard a map published by a consortium of conservancies and agencies, including the Coastal Commission, and he won't believe you. He'll ask for something with an official seal.

And, as Schwartz says, "Obviously, you shouldn't have to carry around a big binder of legal documents."

We had been on the beach maybe 10 minutes when the security guard spotted us. He'd just persuaded another party to pack up and leave.

Oh my God, here he comes. Be cool.

The guard stood out on the beach like a sore thumb, dressed in a white shirt, tie and black pants. The top of his bald head was shiny with sweat. In his hand, he carried his lunch, a clipboard, and a cell phone.

Faster than you can say "Beach Blanket Bingo," he was standing over us.

"This is private property," said the guard, Willis Jackson, who said he works for a company hired by the homeowners association. "You can't be here."

Says who? I let my beach companion, who had official cred, do the talking.

Schwartz had consulted in advance with the Coastal Commission staff and identified the public patches of beach using a map and aerial photographs. We had chosen our spot carefully, in front of a beach house with a swimming pool. According to the Coastal Commission, there's a "lateral easement" there, making that part of the beach public.

Coastal Commission spokeswoman Noaki Schwartz explains that the map shows we are on a "lateral public access" and not private property, as the guard insists.

This appeared to be news to the guard, who gave a long recitation of the wet sand, dry sand rule that seemed to favor the homeowners' point of view.

"It's basically their back yard," he explained.

"I think this part is a lateral public easement, though," Schwartz replied, identifying herself as a Coastal Commission employee and pulling out her Coastal Access map. I also called up Jenny Price's "Our Malibu Beaches" app on my phone, which flashed the word I was waiting for: "LEGAL."

But the guard wanted to see something more official. And then he said he was going to have to call the police.

"When the Santa Monica police department comes out, the first thing they're gonna ask is, 'Are they on wet sand or dry sand,'" he said. "And clearly, you're on the dry sand."

When we wouldn't move, he informed us that we faced $1,500 trespassing fines and lifetime banishment from the beach "so you won't come out here again." And then he walked off to make a phone call, presumably to law enforcement.

It wasn't the Santa Monica police -- we were about 20 miles outside of Santa Monica's jurisdiction. We got the Los Angeles County Sheriff's Department.

It took just 20 minutes for Deputies David Clay and Jim Avens to arrive.

Granted, they were wearing shorts and Clay was walking around in flip flops. They looked more like park rangers than the police. But having to identify yourself to a cop is still unsettling enough to drain the fun out of a day at the beach.

Giving them her business card was one thing, Schwartz said. But when they asked for her date of birth, she felt less like a representative of the Coastal Commission and more like "a mom at the beach with my kid."

Under other circumstances, we probably wouldn't have pushed back. If not for her job, Schwartz said, she probably would have left and never returned.

The private beach enforcers were hoping that's exactly what we'd do, simply give up and move on. So many others had gone, compliantly.

But we were not having it. We drew a line in the sand. We stood our ground. We insisted we were where we had every right to be -- on a public beach -- and had the maps and apps to prove it.

That should have been enough, we thought, and in many places it probably would have been. But not in Malibu. Here, we were strangers. Here, the burden of proof was on us. Schwartz was instructed to email her maps to the sheriff's department.

In the end, the deputies moved on before we did.

I don't know if my friend sent her maps to the sheriff's office. But I do know the homeowners association is going to be getting a letter from the Coastal Commission, informing them that they're violating the 1976 Coastal Act every time they kick people off the public beach.

The letter now has some teeth. Last year, the state authorized the Coastal Commission to fine violators up to $11,250 a day. That makes the $1,500 fine we'd been threatened with look like, well, a walk on the beach.

Still, we didn't feel up for a victory dance in the sand. We felt like criminals, simply because we challenged the desire of some rich people to keep a coveted slice of beach to themselves.

Lucia seemed unfazed by it all, fortunately. She busied herself piling kelp on my feet but kept a watchful eye on the men talking with her mom. After the men walked away, Lucia asked, "Can I go in the water now?"

The answer was yes. And then we stayed for another hour, building sand castles in paradise.