Ruben Navarrette, Jr., journalist, in a Aug. 24, 2015 article, "Just Build Trump's Stupid Wall Already," available at the Daily Beast website, stated:

“For instance, those 1,954 miles cover just about every sort of terrain you can imagine—valley, mountain, desert, river, Indian reservation, private land, state property. Ever try to build a wall on a river, or atop an Indian burial ground, or through the library of a state university? It’s tricky. And once the environmentalists and the EPA get involved, it’s nearly impossible.

Then there’s the fact that no one seems to know what it would cost. In the last six years, estimates for building a fence—which is probably much cheaper than building a wall—have ranged wildly from $1 million per mile to $15 million per mile, depending on where the fence goes. At that price, fencing for 2,000 miles would cost between $2 billion and $30 billion…

[W]alls don’t just keep people out but also pen people in. So those 11 million undocumented immigrants who are already here won’t feel so inclined to go home to Mexico for Christmas or Mother’s Day, like they used to, and where there was always a chance that some of them would stay. Now, unsure that they’d be able to return if they left, they’ll just resign themselves to putting down roots and staying on this side of the border.”

Aug. 24, 2015