What does a ‘secure’ border look like?

FILE - In this May 18, 2006 file photo, a man rests his hands on a fence looking out to the United States from a Mexican customs station after being detained by U.S. Border Patrol in Arizona and returned to Mexico in Nogales, Mexico. The border near Nogales is consider the nation's busiest illegal corridor. (AP Photo/Gregory Bull)Once, the barren mesas and shrub-covered canyons that extend east of the Pacific Ocean held the most popular routes for illegal immigrants heading into the U.S. Dozens at a time sprinted to waiting cars or a trolley stop in San Diego, passing border agents who were too busy herding others to give pause.