IMPERIAL BEACH – Law enforcement officers wanted: must work graveyard shifts alone in remote towns along the Mexican border, put in long hours and perform well in triple-digit temperatures. That message is never touted in U.S. Border Patrol recruitment brochures, but the sobering reality of working on the border has created an environment in which about 30 percent of agents leave their jobs in less than 18 months... The Border Patrol's struggle to keep new hires has become more evident as the agency comes close to meeting President Bush's target of 18,000 agents by the end of the year, up...