It doesn't make sense -- from El Paso to Brownsville.
The Rio Grande is the only water source for fifty miles thru much of that area. A fence that blocked cattle, livestock and irrigation pumps off from the river would make millions of acres worthless and impoverish thousands.
There are smarter, more effective ways to approach the problem. Let's try those, instead, rather than dogmatically repeat the mantra "Build a fence!"
"Create a barrier" to illegal aliens! How about that?
DOES NOT WORK.
We see through that one quite easily. But, tell you what, for all of you who just gotta take your cows to water in the river we'll build the fence around you on the North ~ but NO GATES.
You're on your own.
Shoulder to shoulder National Guard would block the poor little bunny rabbits, too. You're right, high time we knocked down what fencing we have and open up the whole thing. What should we do about the ranchers who have water wells on their property to water their cattle and irrigate their fields (never mind that a good percent of it is unsuitable for cattle or vegetables).