Not that this is a bad idea, but you can't do that; it's illegal. Posse Comitatus prohibits the use of the military to enforce laws. (Immigration policies and prohibitions are civil laws in America.) Congress can change that law, of course, but that would open the door to using the active duty military to patrol our streets every day. Do we really want to go there? Because once THAT precedent is set, who knows who the NEXT president will be? Can you imagine Obama or Clinton with that kind of power?