We can’t very well put a fence on the Mexican side of the border, can we?
And a no-man’s land is not ceding territory to anyone. In fact, it’s doing the opposite. It’s saying it’s under your sovereign control.
My point was that there are some areas where a fence is not needed, Santa Elena Canyon in Big Bend National Park being one of them.
I can’t imagine going to Big Bend and being stopped short of the Rio Grande by a fence. No one gets apprehended there, because few illegally cross there. There’s no where to go.