"ORGAN PIPE CACTUS NATIONAL MONUMENT, Ariz. - Drug smugglers fleeing Mexican police crossed into this desert park and fatally shot a ranger four years ago, prompting That steel-and-concrete wall stops most cars from speeding in from Mexico. But drug and human traffickers have switched to rural entryways into Arizona. Thousands of people now cross on foot. They leave piles of trash, build fires, damage the park's famous cacti and create countless trails through the fragile desert vegetation." "Park workers spend most of their time backing up Border Patrol officers and dealing with border issues. " "But superintendents say the costs...