That and a 200 meter wide field of land mines on he mexican side...
Land mine are controversial and the Pro-illegal factions would just have a field day in court on that one.
Better to use some existing underutilized assets in place of the mines. This proposal would call for using daytime tasked A-10 to patrol the length of the border, while the night time patrol would be tasked to AC-160s ... ROE: free fire zone.