File-This Nov. 4, 2010 file photo shows a Mexican Army soldier standing guard inside a clandestine tunnel connecting warehouses on either side of California's border with Mexico in Tijuana. More than 75 such underground passages have been found along the border since 2008, concentrated largely in California and Arizona. The job of searching these networks can be dangerous, so the U.S. Border Patrol is unveiling its latest technology in the underground war, a wireless, camera-equipped robot that can do the job in a fraction of the time. (AP Photo/Guillermo Arias)