AP Photo

Once, the mesas and canyons extending east of the Pacific Ocean held the most popular routes for illegal immigrants heading into the U.S. Dozens at a time sprinted across the border into San Diego, passing agents who were too busy herding others to give pause. Now, crossing would mean scaling two fences, passing a phalanx of agents and eluding cameras. The difference, Homeland Security Secretary Janet Napolitano has said, is like "a rocket ship and a horse and buggy." In pure numbers it is this: Where border agents made some 530,000 arrests in San Diego in fiscal year 1993, they had fewer than 30,000 in 2012. There is no simple yardstick to measure border security. And yet, as the debate over immigration reform ramps back up, many will try.