Place a string of Brigade size military bases along the length of the border. Erect high observation towers with the latest personnel detection devices. Use motorized hunter patrols to sweep the area at unscheduled times. Designate an area as a detention compound and place all detainees in confinement NLT one week for processing, and return them to their countries of origin with a bill for expenses. OMG!! That’s really cruel and racist of me isn’t it? I haven’t come up with an idea for the 3K+ miles of the Canadian border or the coastal ones yet, but I’m sure you will.
I still think towers every few miles would be very effective. Add to that a squadron of drones with 30 mm M230E1 Chain Guns as used on the Apache as a deterrent and an enforcer to keep those cockroaches out of out country.