The National Guard can only be deployed within the state its based in I think. So basically the Texas, New Mexico, Arizona and California National Guards would do all the work.
Plus there's the ethical question of killing somebody for seeking a better life. And the fact that I don't think that many people will be pumped about shooting people trying to enter their country with the exclusion of those minutemen wackos.
Well I don't think the National Guard should kill the immigrants trying to cross the border. Just rubber bullet them, tazer them, stun grenade them, pack them up into trucks, pack the trucks into airplanes, fly the airplanes to the middle of the Yucatan Penisula.
A probable setup would be to have about 10 meters below the ground to be a solid concrete wall, with sensors, while above the wall would be an electric fence with barbed wire at the top, also with sensors. About every twenty five miles there would be a monitoring station with a battalion of NG troops stationed there, in addition to regular patrols in Humvees, and also have a few dozen Darkstar drones with heat sensors flying at nighttime.