NACO, Arizona (Reuters) - When U.S. authorities raised a tall curtain of steel through this tiny Arizona border town to prevent people crossing illegally from Mexico, the smugglers on the south side were ready.
Using blowtorches and welding gear they burned a rectangular gate in the barrier large enough to drive a truck through, then they sealed it with a padlock to use it at their leisure, border police say.
As the U.S. government pushes ahead with an unprecedented security buildup along the porous Mexico border in this presidential election year, profit-hungry Mexican drug and human smugglers the length of the line are raising their game.
Border police are encountering ingenious and often simply brazen attempts to foil security at both the ports of entry and empty spaces along the nearly 2,000 mile (3,200-km) border by human and drug smuggling organizations.
"The more fencing and the more manpower that they see, the bolder the smugglers are becoming," Border Patrol agent Dove Haber said as she stood by the tall steel wall in Naco, which is patched most days by a busy repair team.
"Before we had the amount of technology and manpower and infrastructure that we have, they were able to operate with some impunity, and they don't want to see that change."
Illegal immigration is a hot topic in the United States, and both presumptive Republican presidential nominee Sen. John. McCain and Democratic Party rivals Senators Barack Obama and Hillary Clinton pledge to secure the porous Mexico border.
The difficulties involved in actually doing so were made clear last week when Ralph Basham, the commissioner of U.S. Customs and Border Protection, said the government might be unable to meet a timetable to gain "operational security" over the border by 2011.
Ongoing measures to erect 670 miles of new fence on the border are credited with helping to cut arrests to some 870,000 last year from 1.1 million. Nevertheless, smugglers are trying and, in many cases succeeding, in breaching every kind of barrier thrown in their paths.
Sturdy steel posts have been sunk in the ground in many areas to stop vehicles crossing north, although drug traffickers have responded by building elaborate vehicle ramps to drive cars over the top, border police say.
"It's like the old show 'The Dukes of Hazzard,' cars flying through the air," said James Jacques, a supervisory Border Patrol in San Diego, Calif.
Illegal border crossers are also routinely beating pedestrian barriers using ladders tailor-made in clandestine Mexican workshops, border police say, while others have used screwdrivers to try to clamber over new 14-foot tall, steel-mesh barriers designed to deny handholds.
One such attempt was foiled. "It took the man a while, and by the time he got to the top, we were waiting for him," said Andrew Patterson, a Border Patrol agent in Yuma, Arizona.
Crossing over the line in remote areas can be straightforward, although the challenge for smugglers and illegal immigrants is to disguise their tracks as they trek north over soft, sandy trails. Here, too, they are proving ever more resourceful, Border Patrol agents say.
Illegal entrants have long used branches to rub out their tracks -- in an old technique borrowed from the Apaches. Some have turned to gas-powered leaf blowers to thwart agents tracking, or "sign cutting," for them on roads running parallel to the border.
"One smuggler we caught would cross two, six, ten, 15 people in a group, and every time he crossed a road, he would blow out their 'sign' with the yard blower," Jacques told Reuters in an interview.
Professional smugglers have for years also wrapped their feet in carpet offcuts or strips of foam to try to slip north without a trace, and have laid boards and ladders to cross dirt roads monitored by the Border Patrol.
Other scams include smugglers taking their shoes off and hopping rock-to-rock in a bid to leave no tracks; putting their shoes on backward to try to confuse pursuers, and even attaching boards studded with horseshoes to pass as animals.
"They think it looks like hoofs," agent Haber said of this scam, which proved unsuccessful. "But the stride of an animal and a human are not the same. A horse would be having to take a lot of very, very small steps to look like a human."
Smugglers are not only adapting to tougher security in the empty spaces of the border, they are using a seemingly endless variety of wiles to try to beat detection as they pass through the ports of entry, some of them new, many of them recycled.
In addition to special compartments in car tires, gas tanks and door panels to hide drugs, U.S. Customs and Border Protection inspectors at ports of entry in New Mexico and west Texas recently found marijuana submerged in jars of jalapeno pickles, stuffed into mattresses and even hidden in Christmas holiday candles.
At crossings in California, meanwhile, inspectors in recent years have found a child smuggled inside a sealed papier-mache pinata doll, illegal immigrants crammed inside vehicle seat covers, and, late last month, two Mexican women smuggled in a pickup trucks' engine compartment through Calexico, Calif..
As controls tighten, criminals slipping over the line have also tried to thwart digital scanners linked to immigration and law enforcement databases by burning off their fingerprints, smearing with them superglue, and even, in the case of one man, having them surgically replaced with skin from their feet.
"It's an ongoing battle," said CBP spokesman Brian Levin. "I used to say I thought I had seen everything, but there's always something new."
Reporting by Tim Gaynor; Editing by Eddie Evans