ARIZONA: Daily, US Border Patrol agents in San Luis, Arizona 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