"Well, it’s not," Perry agreed, adding it might not only in the literal sense. "It’s a wall, but it’s a technological wall, it’s a digital wall. There are some that hear this is going to be 1,200 miles from Brownsville to El Paso, 30-foot high, and listen, I know you can’t do that."
A physical wall works just fine from El Paso overland to the Pacific. But you ust don't build a physical wall along a river -- especially if it's the only water source in a semi-arid region. Ranchers and livestock and wildlife on both sides of the river need unhindered access to the water.
That's not to say that a secure barrier can't nonetheless be erected. The Israelis have a similar problem when the Jordan River is the only thing separating them from Jordan. There is no fence along this border, save for a common 6' fence of hogwire, mounted on metal posts and topped by two strands of barbed wire that runs about a quarter-mile back from the river. There are frequent gates, most of them left open.
The real "wall" in this case are Israeli border guards supported by high-tech devices -- sensors, cameras, etc. -- and are highly mobile, with ready access to previously developed strong points and firing positions. If it works for Israel on the Jordan, it can work for us on the Rio Grande.
Thus, the Rio Grande border can be effectively secured without a wall...if Trump wants to do it.
Maybe it would be more effective just to hire more border patrol agents, and improve the electronic surveillance. If Trump builds an "electronic wall" -- and it's effective -- he can count that as having delivered on his promise.
Perhaps more important than the wall itself, though, is to stop the acceptance of illegal aliens once they get inside. If they know they'll be sent back, they'll quit coming. (Except for terrorists, of course, who have no intentions of staying -- the ones backed by sophisticated organizations will still be able to come in by plane or boat, as with illegal drugs. With borders as long as ours, there's no practical way to wall ourselves off from everything. We can, though, stop the mass influx of illegal aliens.)