The only other options are to build the wall along the river, cutting all of the ranches on the US side off from the water, or build it in the middle of the river. Neither is going to happen.
“The only other options are to build the wall along the river, cutting all of the ranches on the US side off from the water”
Plumbing was invented thousands of years ago. I hear the technology is still used in some places.
Middle of the river would be ideal. No interference with watering livestock, while making climbing a wall that much more difficult. In fact, build a dam at the mouth from the wall in the middle to the north shore and let it fill to its historical high level and maintain that. Maybe locks every hundred miles so it is navigable all year for barge traffic. Better livestock watering, irrigation source, transportation, hydro power, and border security all-in-one.