There is a lot of land along the border that would be suitable for military gunnery ranges and artillery practice.
The Barry M Goldwater Bombing range stretches along the border from Yuma to the Organ Pipe National Monument. BMGR West is run by the Marine Corps, and BMGR East is run by the Air Force. Yuma Army Proving ground is 30 miles north of the border. The Chocolate Mountain Gunnery Range in Imperial and Riverside Counties in CA is 35 miles from the border. All of these ranges are live fire and all have issues with illegals and drug runners crossing them. The prospect of being turned into pink mist does not deter these people. The Border Patrol is out in force on all of these ranges also.