“Good fences make good neighbors,” wrote the poet Robert Frost.

And he was right.

President Trump has been pushing for barriers along the U.S.-Mexico border. And the newly installed fences are doing their jobs.

On Sunday, Border Patrol agents were forced to rescue three foreigners who got stuck on top of one of President Trump’s border wall in San Diego.

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“The man and two women tried to use dense fog to cover their attempt to climb a section of 30-foot-high fence — part of nearly 100 miles of replacement wall built under Mr. Trump,” The Washington Times reports.

They cleared the primary fence up along the border but became stuck atop the fog-slicked secondary fence, which is set back from the boundary line, creating an enforcement corridor between the two fences. It’s not clear how they managed to scale the two walls, though Customs and Border Protection suggested they likely had smugglers who were helping them but then abandoned them when they got stuck. Agents called out the San Diego Fire Department, which had to use a truck and lengthy extension ladder to get the migrants down.

The Times said there have been plenty of falls from the high fences along the border. Supervisory Agent Jeffrey R. Stephenson told the paper that “The falls have led to numerous serious injuries including broken legs, broken ankles, skull fractures, brain bleeds, broken scapula, fractured vertebrae and appendicitis.”

The bollard-style fence in San Diego replaced what was known as “landing mat fencing, an outdated design that used thin metal plates that were easily breached,” said The Times.

In September, Trump, joined by top Homeland Security officials, visited California’s border with America’s neighbor to the south, where he called the 18- to 30-foot barriers “an amazing project” and “virtually impenetrable.”

“This wall, you won’t be able to touch it. You can fry an egg on that wall — it’s very very hot,” Trump told reporters in Otay Mesa, in the San Diego sector of the border. “So if they’re going to climb it, they need to bring hoses and water and I don’t know where they’re going to hook it up. There’s not a lot of water out here.”

On his visit to the San Diego-area border, Trump showed off a section of the 30-foot-tall bollard barrier that U.S. officials are building.

“Look at the inner tube to see what happens, because after the wall is up, we pour concrete and concrete goes into the tube, and in addition to that we have rebar,” Trump told reporters.

“So if you think you’re going to cut it with a blowtorch, that doesn’t work because you hit concrete,” he added, “and if you think you’re going to go through the concrete, that doesn’t work because we have very powerful rebar inside.”

“When the wall is built, it will be virtually impossible to come over illegally, and then we’re able to take border control and put them at points of entry,” Trump said.