“Ranchers also
depend on Rio Grande water
for their livestock...
I’m sure something could
designed that wouldn’t catch
debris or impede the flow of
the river. “
Concerned about a dam river? May be they need to find alternatives to the river for water. Unless Mexico allows the wall on their land, the wall has to go on the US shore, so it must cut off access to ANYONE attempting to get from the river to the US land. That includes preventing snakes, lizards, frogs, cows and humans.
I have seen sheetpiling which could be adapted for the river. Sink a base or 4” gap tubes themselves. Water, snakes, and kittens, or other dear things could pass.