The U.S. now uses only drones to patrol almost half the Mexican border, in a shift to control desolate stretches where there are no agents, camera towers, fences, or ground sensors, the Associated Press reports. The government plans to expand the strategy to the Canadian border. The patrol setup is a significant departure from a decades-old approach that emphasized boots on the ground and fences, and the purpose is to assign agents where illegal activity is highest. Under the new setup, Predator B drones sweep remote mountains, canyons, and rivers with a high-resolution videocamera and return within three days for another video in the same spot. The government has operated about 10,000 drone flights under the strategy.