Actually, this is the way that it SHOULD be done.
An "outer wall", a "no man's land" strip, and an "inner wall".
Here's a pic I took of the Berlin Wall in 1971:

The pic was taken from "The West", looking into East Berlin.
It shows why "the wall" was MORE THAN "just a wall", but an effective system to deny passage.
Of course, here the outer wall would need to be more like this:

But again, with a "median", and an "inner wall" as well.
Are we going to be serious about protecting our borders, or not...?