#1. A Series of Walls, Fences, Drones, and, remote cameras, detection equipment, etc.
#2. Allow Ranchers, and Land owners to make "citizens arrests," of those who come across their land. At the VERY LEAST, put some legal teeth into "NO TRESSPASSING" laws....
#3. Set up a few "Base Camps" for the numerous National Guards out there, who occassionally go to train in parts of Arizona and Nevada to acclimate to "desert conditions." Simply rotate Guards in and out of BORDER Base Camps. The mere pressence of more organized military will dissuade some. Perhaps have "training" (NON-LETHAL, of course), in which these Guards men patrol, capture, and detain those comming across illegally.
#4. BAN and destroy any and all of the "water stations," etc. set up by dogooders, to make it as easy to tresspass as possible.
#5. And, while I understand we will NEVER do this, I feel it would be one of the BEST Deterrents: Make WAR on the Cartels and Coyotes who smuggle both people, and drugs over the border. Capture a few of these Coyotes, who carry people across in trucks, often in incredibly dangerous conditions...pull them out of their trucks...take them to the side, and, shoot them in the head. TELEVISE it. Trust me...the Coyotes will diminish greatly in numbers. Same for the Drug Trade. Either the Cartels will cease and desist, or, the price of illicit drugs will skyrocket, as part of the costs....
#6. On the OPPOSITE END (This will NEVER be done, either...), streamline and fast track immigration, and/or work visas for MEXICAN citizens. Then, go down the list to other nations in Central and South America, where many of these illegals are comming from.
OR,
We could just invade Mehico. EVERYONE, except for Corrupt Mexican Politicians, and Gang Lords, would be BETTER OFF!
EVERYONE.
So, I suppose, that is the best reason NOT to do anything....