When the official border is the center of a river where do you put the fence? From El Paso to the West coast you don’t have that problem in fact a fence and right of way is already in place. I have friends and family that own several miles of land on the river and they will not accept being fenced off from river access. The river is the only reason much of that land is worth ranching, without full access entire ranches will be useless. Build the wall from El Paso west and step up security on the Texas border. We have military bases in Texas and the border would be a great place to practice and train.
I’m assuming a government owns its own borders.
At the same time I believe there can be accomodations if creative people think about it.
An aqueduct can be built, or some other form of irrigation/supply line, to ensure that local landowners and their livestock have access to water.