Backstory: Inside 'Border Patrol, Inc.'

Inside the border patrol, they're called the "rock group" - agents, trained as welders, who spend days repairing holes in a 15-foot-high steel wall here along the border to keep out illegal immigrants. Both human traffickers and drug smugglers pay Mexican boys to use hacksaws - sometimes working all day - to cut holes in the wall, an "iron curtain" made out of salvaged aircraft-carrier landing mats. The welders respond with molten metal.

But while they're working, the agents are frequently pelted with rocks by youths on the Mexican side of the controversial wall. Hence the rock group moniker - a reference to the mini-intafada here rather than any parallel with Mick Jagger. The "boys are hurling stones today, so be careful," one agent warns us as we tour the area.

The tale of the hacksaws and the welders is a metaphor for life along the dusty US-Mexico border in an era of heightened security and expanding illegal immigration.

Up and down the 2,000-mile border, the US government is throwing more manpower and sophisticated technology into slowing illegal entries into the US. But as it does, immigrants are showing greater ingenuity in circumventing the barriers and patrols.

Now, as Congress considers another overhaul of immigration laws, the encounters and clashes along the border are likely to intensify. Most of the bills in Congress include provisions to expand the border patrol (now part of US Customs and Border Protection), which has already seen agent strength along the nation's southern flank more than double since 9/11, to 11,000.

The result is an agency that is becoming increasingly complex and unwieldy. Agents already use everything from horses to mountain bikes to all-terrain vehicles to track drug smugglers and human traffickers. They also use aerial surveillance, periscope trucks, and underground sensors. Yet, through it all, the task of stopping illegal immigration can still seem daunting, if not futile, as a day in the life of the border patrol here recently showed.

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The nerve center of operations in the Tucson sector, a 261-mile stretch of border, is an expansive new brick-and-glass headquarters in Nogales. In one room - the intelligence hub - sits a U-shaped set of desks with 25 television monitors that show various grids of the desolate desert area. The new technology employed along the border - movement sensors buried amid the mesquite, cameras, and two unmanned aircraft - transmit information instantly to the monitors.

Camera 17 is trained on someone walking along the border fence. He suddenly spots the roving eye and ducks behind a tree. Camera 35 shows where an underground sensor has gone off, so the agent dispatches a crew to "lie in wait" for the crossers. They will pack in on horseback or on four-wheelers. Sometimes it takes two to three days to reach the spots - and the waiting can be inhospitable. One agent, Shannon Stevens, recalls her first ambush duty: She was stalked by a tarantula.

In another room, the walls are decorated with photos of confiscated items - knives, shotguns, 4,391 pounds of cocaine from a bust. Here, junior agents attend classes in Spanish and immigration law one day a week for 10 months. They're tested twice. If they fail, they lose their job. The lessons are a follow-up to the 19 weeks the agents spend at an academy that includes the equivalent of three years of college Spanish. Jim Hawkins, a senior agent, says the border patrol receives 40,000 applications a year. Only 2,000 to 3,000 survive screening and training.

Another room in the building is reserved for confiscated drugs. On this day, agents have loaded some 5,000 pounds of marijuana into two Penske moving vans and sent it north to Tucson for burning, which happens once a week.

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To stem illegal entries in Nogales, the agency is trying a "defense in depth" strategy. It involves blocking smuggling routes through the town with the lit up "iron curtain" - and pushing the traffickers farther out in the desert, where agents have two or three days to track them. The idea is also to avoid shootouts in populated areas.

On the ground, the agency is bolstering surveillance with a new "scope truck." It looks like a Chevy camper. But the roof has been cut out and a large infrared camera sits in the back like a periscope. Controlling it with a joy stick, agents can see illegals at night as far as six miles away.

We leave headquarters and bump along a road for several miles that follows a border ridge through the Coronado National Forest. Only three strings of barbed wire separate the US from Mexico here. The Mexico side is on high ground - rolling hills dotted with oak and walnut trees that provide cover for smugglers. Although no people are crossing, worn paths littered with empty water jugs wind across the border at frequent intervals.

We circle back west and head through the city, where houses are painted in pastels. Hawkins points out what he calls the most troublesome drug-smuggling neighborhood in Nogales. A supposed drug lord's large hacienda sits among scores of shanties.

Farther east we reach Hamburger Hill, a notorious smuggling route. Below, the welders repair the fence. Their truck is fortified with mesh cages to protect the windows from the rock throwers. Sometimes the stoning is just a diversion, Hawkins says: While the youths throw, a smuggler crosses a short distance away.

"Manpower alone is not going" to stop this, says Rodolfo Espino, a political scientist at Arizona State University in Tempe. "As long as there's a pull for employees on this side of the border, there will be a constant push to enter from the Mexican side."

Driving back through Nogales, the agents note other ways illegals gain entry. Underneath two dry washes, which the border patrol filled in to prevent crossings, the immigrants crawl through a metal drainage culvert. To stop this, agents fabricated a steel door for the pipe. The smugglers retaliated with hydraulic jacks. The agents responded with sensors, cameras, and flood lights. It's keeping the smugglers at bay, for now.

"It's a game of constant adjustments," sighs Hawkins.