Today, on that border is double fencing, stadium lighting, surveillance cameras and motion detectors. It's the most heavily fortified five miles of the border - all monitored from a command center near San Diego, CBS News correspondent Bill Whitaker reports.
"Over the years the San Diego sector has been able to incrementally gain operational control of this area," said Michael Fisher, the San Diego sector's chief patrol agent.
Proof? The number of people caught crossing illegally has dropped dramatically from 600,000 a year in the early '90s to just 153,000 last year.
Fewer apprehensions means fewer people sneaking across, says the Border Patrol.
But not even all of the fencing can fully shut down the illegal flow.
There are two fences, lights, cameras ... and a lot of action.
"A lot of action, absolutely," Fisher said.
For every action there's an opposite reaction. Put up a fence and "they can be up and over, in some cases in less than a minute," Fisher said.
It's frustrating and expensive. Only 670 miles of the 2,000-mile border are to get fencing and that's behind schedule. The price tag: $1.2 billion, says the Border Patrol. That's up to $3 million per mile.
But factor in life-time maintenance and congressional researchers say the price could top $50 billion.
Today, almost every mile a different fence - short, tall, mesh, bars - intruders defeat every one. They even use car carriers to drive over.
If not over, under: 21 tunnels have been discovered under the border since 2000. There are brazen ways to drive through. One man came sewn into a van's seat.
So, it sounds like no matter what you do, you're finding a way around it.
"Yes, they are - or they're trying to," Fisher said.
And that's where there is a fence. A state away, near third-generation cattleman Richard Hodges's ranch south of Tucson, Ariz., there are miles and miles of open spaces along the U.S.-Mexico border. Only rusty barbed-wire divides the two countries.
"But that is no deterrent for anybody to come across," Hodges said.
The government promises a virtual fence of sensors and cameras for areas like this, but with that still on the horizon, those controversial border-watchers, the Minutemen, are building a $650,000 real fence along Hodges' mile of border to keep illegal crossers out.
"But won't they just move on down the road to the next property?" Whitaker asked.
"They will, they will," Hodges said. "It's just not going to stop as long as there's a market for illegals."
Whitaker met a coyote, a small-time people smuggler, across the border in Tijuana. He asked CBS News to conceal his identity. He boasts that he gets 40 people a week into the U.S. - most through the fortified zone near San Diego - at up to $3,500 a person.
He said, through a translation, "You can build three or four fences along the border, but people will continue to cross because of the magnet of work."
Most Americans think putting up a fence is going to stop the illegal flow. But is it?
"No, not in and of itself," Fisher said.
But Fisher says a smart mix of fencing, technology and manpower can do for the entire border what it's done in San Diego.
"What we've done is we've increased the probability of apprehension," he said.
The question is, will a nation demanding total control of its borders be satisfied with less.
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