We have infrared satellites, drones, the most sophisticated military, and most advanced law enforcement in human history. If we're just talking about the border from Brownsville-to-Tijuana, then fucking fund it. The Border Patrol need funding. They need manpower. I don't happen to believe that immigrants, legal or not are a problem for America. Honestly, I'll even come right out and say the very concept of "You're not welcome here" is intrinsically unAmerican.
But, from a practical standpoint? It would cost $Trillions less to secure the border with technology than to not secure it with the Mongol's plan. (To keep out the Hun.) We learned that, from China, in the Ming Dynasty! Walls don't work. Period. Hell, Romulus (Mythically) demonstrated that shit.
If you ask me, we should devote more resources to ensure that they can get across the border, safely, and legally integrated into society. The problem with that is Racism. European Americans don't want America to become more Latin American.