They call it a wall, but technically, it's a fence — albeit an imposing one. And in Nogales, Ariz., it's impossible to miss.

Eight metres tall in most places, it slices through the town along the international border between the United States and Mexico. On a directive from U.S. President Donald Trump, the fence is now fortified with coils of razor wire, installed earlier this year.

And still they come: migrants, families fleeing strife in Central America and drug smugglers who all find a way through, over, under and around the infamous wall.

It's a frustrating fact of life for U.S. Border Patrol agents.

"We know that if you build a 100-foot wall, they're going to bring a 101-foot ladder," said Jake Stukenberg, one of the agents stationed in Nogales, about 100 kilometres south of Tucson, Ariz.

But, he said, at least the wall slows them down.

Stukenberg agreed to spend a day with CBC News earlier this month while patrolling the 50-kilometre section of border his unit is responsible for to underline the challenges inherent in policing a barrier that faces a seemingly never-ending flow of migrants and smugglers determined to get across — no matter what.

About 1,000 border crossers are caught trying to cross the border in Stukenberg's district every week, he says.

U.S. Border Patrol agent Jake Stukenberg at the border outside Nogales. (Paul Hunter/CBC)

Those fleeing strife typically seek out agents and immediately claim asylum. Stukenberg says he sees plenty of people like that, including a group of more than 100 one day this month. But, he says, a key focus for Border Patrol is those who try to avoid capture.

Drug smuggling has long been a big part of the cross-border challenge in Arizona. In years past, the smuggled drug of choice was marijuana, but Stukenberg says, lately, they increasingly see fentanyl, the powerful opioid behind a rash of overdose deaths in recent years in the U.S. and Canada.

And despite the imposing nature of the wall, smugglers are adept at breaching it.

Razor wire along border fence near Nogales has been cut by fence-jumpers. (Paul Hunter/CBC)

"This is one spot where they cut it," said Stukenberg, pointing at one of the visible gaps in the razor wire left by those who climb up and use cutters to snip a pathway for those who want to get to the other side.

At that point, the race is on.

"It is literally seconds from the time that someone jumps over that … fence right there, puts their feet on the American soil and runs up to those areas," said Stukenberg, pointing at a nearby Nogales industrial park.

"And there's a million hiding places in there. So, it's literally 30 seconds before they could be in a hiding place. Good luck finding him after that."

On the day CBC News spent with Stukenberg, agents in his jurisdiction detained 154 suspected undocumented migrants. One such detention happened just a block from Border Patrol offices, as CBC News drove up to meet with Stukenberg.

U.S. Border Patrol agents detain an alleged undocumented migrant at the Arizona border with Mexico. (CBC)

Evidence of the migrants is everywhere. Abandoned clothing is seen tangled in the razor wire; there are clear handprints on the bollard-style fencing, left by those who've climbed up and over; and seemingly everywhere there is fencing, there are also abandoned water bottles left by those who had travelled through the desert just to get to that border.

Stukenberg says he leaves politics to the politicians, but he doesn't hide the fact he's very much pro-wall. Trump has vowed to buttress and extend existing barriers, de facto creating a wall along the full length of the more than 3,000 km long U.S-Mexico border.

Stukenberg says the fence along his stretch of the border makes his work easier simply by impeding those who want to cross illegally, even if it doesn't always stop them.

"Give us the tools necessary to do our job," he said.

A jacket is seen stuck in the razor wire of the border wall. (Jason Burles/CBC)

What's his broader answer to the challenge of dealing with all the migrants and smugglers?

"If I had a magic wand?" he said. "I would eliminate the cartels … from the face of the Earth.

"Then you get rid of the No. 1 facilitator for narcotics into our country. You get rid of the No. 1 facilitator for illegal immigration. You get rid of the No. 1 facilitator for corruption in other countries."

But Stukenberg isn't holding his breath.

A training tunnel is buried about two metres underneath a parking lot at the Border Patrol headquarters in Nogales. (Paul Hunter/CBC)

Patrolling down below

Meanwhile, as he patrols the border along the dirt roads that parallel the wall, other agents train for illegal crossings of another kind — underground.

Fellow agent Kevin Hecht took CBC News into a faux smuggling tunnel constructed as a subterranean training ground.

It's buried about two metres underneath a parking lot at the Border Patrol headquarters in Nogales. It's dark, cramped, filthy — and instructive.

"It's all belly-crawl," said Hecht, highlighting how narrow it can be inside the actual tunnels.

Smugglers will often dig through dirt until they reach municipal water drainage tunnels, then break in and shimmy into the U.S.

So, patrolling agents are on the lookout for cuts in the tunnel walls.

U.S. Border Patrol agent Kevin Hecht inside the training tunnel. (Jason Burles/CBC)

"You have to go and look at the pipe, look for any change in the pipe," said Hecht.

Scuff marks can signal patched-over places where smugglers have installed, in effect, doorway flaps.

"And behind it will be an illicit tunnel that you can crawl through across the border. That's what they call interconnecting," he said. "And then once you're in this pipe, you're on the U.S. side of the border."

Smugglers will often dig through dirt until they reach municipal water drainage tunnels, like this one, then break into those tunnels and shimmy into the U.S. (Jason Burles/CBC)

Drugs come in through the existing water drainage tunnels, but agents in Nogales also come across tunnels that are fully dug by hand, including one just this past May.

Back on top, Stukenberg signalled toward a grassy hill on the Mexican side of the wall.

"I absolutely would be amazed if we're not being watched right now," he said.

Spotters regularly keep watch on Border Patrol agents waiting for their vehicles to leave a particular location before instructing drug or human smugglers to make their jump over the wall. (Paul Hunter/CBC)

Spotters regularly keep watch on Border Patrol agents, he says, waiting for their vehicles to leave a particular location before instructing drug or human smugglers to make their jump over the wall.

"The smugglers will sit on this hill," he said, pointing, "[and] guide people with cellphones."

Soon enough, Stukenberg sees movement in some faraway bushes.

"I'm spotting a scout right now," he said. "Under a tree. Two people, three people."

And suddenly, they appear, making their way down the hill and toward the border fence. Border agents watch and wait. But then the people disappear into a gully.

"They're definitely smugglers, or being smuggled," said Stukenberg.

It could be hours yet before they try to cross.

"They're cartel," he said. "They have a big budget, and they have all the time in the world."

Stukenberg patrols the border west of Nogales in his vehicle. (Paul Hunter/CBC)

But as Stukenberg waits, his radio crackles with word from other agents patrolling another part of Nogales who are suddenly caught in a car chase involving suspected human smugglers.

Stukenberg puts his vehicle in gear and scrambles to go help.

"They've bailed out of the vehicle and … are running into the desert," he said, spinning his vehicle around at the border wall and heading into town, all the while knowing the spotters on the other side will quickly take note and relay word to whoever was down in that gully.

It happens all the time, he says.