Well...I will add this note. If you go and look at the East German Wall...it was always defeatable. With guard patrols, mined fields in front of it....it didn’t matter...folks would figure out the angle...sometimes even digging under it, and reach the other side.
The wall is the one impediment to border crossing that the next Barack 0bama cannot dismantle simply by issuing his own EO. And the Berlin Wall very much did impede immigration into the West. People had to go to extraordinary measures to defeat it.
I’m not concerned with a wall not being a perfect deterrent. I’ll accept “pretty good”.