I’m not opposed to border security, and a high wall may make sense in some remote areas, but Beto is right about that stretch along the Rio Grande
First, much of the land on our side is owned by private landowners, each of whom would have to be subjected to eminent domain processes. Eminent domain can be challenged in court. Not only could that be a long, dragged-out process, but if even one challenger wins, there would be a big opening in the wall! And the USA can’t just take a narrow strip of land like a railroad path. There has to be room on the river side for flood control, repairs and patrols. There also has to be room on the other side for patrols and repair crews. There will have to be a second wall built by any ranchers that have livestock in order to keep them out of the strip of federal land, and out of the way of border officers making their rounds. (That may or may not be at government expense. The ranchers and the state of Texas may have to build their own barriers from the newly-formed federal territory.)
Second, the actual border between the USA and Mexico is in the middle of the river. Therefore, any immigrants who cross the river would have reached USA territory before they get to the wall, and could then claim asylum, and/or deliver an anchor baby without even reaching the border wall! Therefore, border patrol officers would have to patrol the river side of the wall as well as the area beyond the wall.
I very much doubt that anything will ever be built there, and if it is, it will probably be far in the future.
And even if it does happen, it will cause more problems than it solves.