Ten or so rows of concertina wire ten feet high, in a hundred foot swath running the border with guard towers and electronics and rapid response teams every twenty miles.......or whatever works. Forget the high wall. Drill in some vertical pipes to slow down vehicles the entire route as well.
Fencing, guard towers, sensors, camera's, drones. One standard two lane concrete road running the inside fence.
Little concrete expense outside the road. Put the military to work protecting our southern border, a very vulnerable and strategic attack point. We need them there anyway, given the threats being made clear.
Build that highly functional system in no time at all. And the expense would be minimal in comparison to a concrete wall.
Let Trump make the guard towers, barracks and support sites be ultra deluxe for the teams stationed there. Set a barracks up for every X amount of guard towers, with a rapid response plan for the men off duty. Three teams per tower, one on station, two at the barracks, each barracks handling X towers. Layered, efficient, inexpensive, highly functional, overlapping support. Make the towers strong, safe, and comfortable. Make it a sought after duty.
Build a nice rifle range at every one of them. Put full size targets out, way the heck out there. Encourage this duty as an opportunity to refine one's marksmanship. Let them compete. Heck it would be easy to create a series of targets that are hit / miss with sensors that score. One could actually have a shooting competition for each duty shift across the entire border. How fun would that be.... Of course the targets would be within the wires to make sure it was safe.....
Educate others to grow our base of informed citizens, it's tyranny. Spread the Gospel.
Prepare wisely individually. An army runs on it's stomach.
Network with those who prepare wisely and take advantage of the strength in numbers and the economy of scale.
Then, when the curtains come down and the truth is evident to an informed citizenry, we unite and fight the new world order.