Then I would suggest that you re-read your Roman history.
Generally, Rome built walls around forts and cities with varying lengths of 1 mile to 12 miles. Two walls were approximately 35 miles long. The Hadrian Wall was approximately 70 miles long. All of them together didn’t equal the 2000 miles of border we have to secure.
Likewise, Rome’s enemies didn’t have the capabilities to breach those walls on a daily basis. They couldn’t drive trucks though them or use battery-operated saws to cut through them. Do you know why Roman walls, generally speaking, worked? (The walls did eventually fail.) Rome manned their walls. Roman soldiers lived on those walls.
There is no comparison between heavily manned, sturdy Roman walls that were 45 feet tall and 12 feet thick with our unmanned, steel border fence that is 12 feet high and mere inches thick. The proposed construction of the southern fence is a joke. It won’t stop anyone who really wants through it, over it, under it, or around it.
But if you think we should build 2000 miles of 45 feet tall, 12 feet thick walls that also extend into the ground the same depth and width as their above-ground halves, I’m totally in. That’s a wall worth building. It’s not a fence. But it has to be manned or it’d be a waste of time and money to build it.
And if we are going to go that route, why not shoot for the moon and build our own version of the Panama Canal from the Gulf to the Pacific Ocean? That type of barrier would become an economic boom for us with all of the shipping traffic we’d get. And it would physically separate the U.S. from Mexico to such a degree that there would be no battery-operated saws, no ladders, and no tunnels. Problem solved.