And while I might sound like a whacko environmentalist, there are also many critters who live in the desert who need access to the river and would be cut off by a fence.
You are correct. The border fence argument is to me very shallow. In remote areas, there would be more tunnels under it than in my backyard from the moles and gophers. It would be a huge waste of money. I say more boots on the ground and drones.