A wall keeps unauthorized people out. Using drones to kill the unauthorized people (skynet) is an extremely inhumane idea.
You are caught trying to invade, or have overstayed your visa or become a societal leech and we dont want you any more.....a quick injection and graphic demonstration of exactly how it works and you are bussed 1/2 click south of the transmission zone and set free, YES, FREE AS A BIRD to pursue your life, liberty and all the happiness you can find, somewhere else besides in the United States.
Phase two of the project is a fleet of roving radio trucks that canvass the country north of the transmission zone, concentrating on seaports of entry, airports and other common areas where common trash co-mingle, randomly emitting detonating radio bursts to "police" any undesirables who may attempt safe reentry by shielding or other seruptitios means.
Hmmmm! After a couple dozen, the traffic would slow down.