Don Bartletti / Los Angeles Times
Ramirez, left, and Hernandez nervously scan a phalanx of fences that fortify where the boundaries of California, Arizona and Sonora, Mexico, meet. A downward trend in arrests of illegal immigrants began at about the same time the U.S. started fortifying the border with more agents, fencing and infrastructure. But border enhancements alone aren't enough to stop immigrants. The U.S. economy provided further disincentive.