SAN LUIS, Ariz (Reuters) - Daily, U.S. Border Patrol agents in this Arizona town faced groups of up to 200 illegal immigrants who would swarm across the border from Mexico, sprinting past the agents to a new life in the United States.
That was until 18 months ago, when the single fence was bolstered by two taller, steel barriers, watched over by video cameras and lit by a blaze of stadium lighting. Now the incursions known by the agents as "Banzai Runs" have all but stopped.
"It was overwhelming," said agent Andrew Patterson. "This used to be a huge trouble area, now we are almost down to zero."
The troubled patch of borderlands in this speck of a town in far west Arizona is among many places along the almost 2,000-mile (3,200-km) U.S.-Mexican border that are getting new fencing as part of a U.S. initiative to stem the flow of illegal immigrants.
Washington plans to build 670 miles of barriers, including pedestrian and vehicle fences, by the end of 2008. So far, more than 300 miles have been built, and the government is pushing hard in this election year to finish them, as mandated by the U.S. Congress.
While they are controversial -- some border landowners resent what they see as unwelcome government intrusion and some conservationists argue it disrupts wildlife flows -- border police say this stretch of new fencing has been highly effective.
"It has been a massive success. It has allowed our agents to gain control over the area and acted as a deterrent for people thinking of crossing," said Jeremy Schappell, a spokesman for the Border Patrol's Yuma sector, which includes San Luis.
Illegal immigration is a hot-button topic in the United States. A pledge to secure the porous southwest border with a combination of new barriers, increased manpower and new surveillance technologies is routinely made by both Democratic and Republican candidates seeking to be their party's pick to run for president in November.
The barrier erected in San Luis is similar in design to those pioneered in San Diego, California, and El Paso, Texas, in the 1990s, which helped the Border Patrol regain control of what were then the most heavily transited areas of the border, crossed by hundreds of thousands of illegal immigrants each year.
The El Paso barrier -- two parallel chain link fences over 15 feet in height spaced 30 feet apart along the bed of the Rio Grande -- helped cut the number of illegal border crossers and curbed crime in the city, residents say.
The barrier has no barbed wire and includes several formal breaks, one where a freight train crosses from Ciudad Juarez, in Mexico, another to give access to the river bed, and is watched around the clock by border police spaced at intervals along the line.
But without 24-hour monitoring, as well as the stadium flood lights, and the directional cameras linked to a central control room manned by National Guard troops, the El Paso fence would be little deterrent.
"Along this stretch, the fence in itself doesn't stop anyone, but it does slow them down and gives us time to react. Those extra seconds are vital, and that's what a lot of people don't realize," said agent Jose Cisneros.
"You don't just put up a fence and say that is the end of it."
Graffiti is scrawled on the Mexican side of the gray concrete bed of the Rio Grande, while huge, cross-border highway bridges run over the top.
Every day, agents in El Paso face off against Mexican people smugglers who form groups to wait on the banks of the Rio Grande in broad daylight and wait for a moment to storm the fence, and sprint the few yards (meters) to the streets of El Paso.
"While in the countryside they cross under coverage of darkness. In the city, they wait until daylight so they can blend into the city population," Border Patrol agent Joe Romero told Reuters reporters during a recent tour of the area to see the barrier in action.
Reuters' correspondents witnessed two men crawl through the shallow, muddy Rio Grande and up the bank through the shaggy undergrowth on the U.S. side. There they climbed over the first fence, waded through a concrete irrigation canal and squeezed through a gap under the second fence, before running across the busy highway and into El Paso, where they were arrested.
"Whenever they think an agent is distracted or a camera is down, the smugglers tell the aliens to go for it," Romero said, highlighting the need for vigilance and rapid response for the fences to be effective in this urban strip.
"We are talking 10 to 15 seconds from the edge of the Rio Grande to the housing complex on the other side of the highway," he added.
As new barriers -- including single, double and triple layered pedestrian fences and lines of hefty steel posts sunk into the ground to stop vehicles -- carve out over hundreds of miles (kms) of borderlands amid political pressure for an end to illegal immigration, not all stretches of fencing are proving to be as effective.
A new single layer of steel mesh fence 10-13 feet tall stretches out across the rugged, high plains deserts and grasslands on either side of the small town of Naco, Arizona. The Border Patrol credits it with contributing to a fall in arrests, but some residents say it has done little to stop illegal immigrants.
In two recent visits to the area, Reuters correspondents found an improvised wooden ladder and stretches of garden hose used to scale the barrier, along with dozens of pieces of clothing and rucksacks apparently tossed by illegal border crossers as they breached it.
Local rancher John Ladd said some 300 to 400 illegal immigrants continue to clamber over the new steel barrier flanking the southern reach of his farm for some 10 miles (16 km) each day, as an effective combination of technologies and manpower remains elusive.
"It's so easy to climb that I've seen two women that were pregnant, I've seen several women in their sixties and all kinds of kids between five and ten years old climb over it," Ladd said, as he leaned on a section of the steel mesh fence that stretches like a rusted veil westward toward the rugged Huachuca Mountains.
"They're getting some help, but when you put it in perspective, its pretty amazing to have a nine-month pregnant woman climbing over that son of a gun, and thinking that this is going to be the answer to solve our immigration problem."
Reporting by Tim Gaynor; Additional reporting by Robin Emmott in El Paso, Texas; Editing by Eddie Evans