The wife and I were Big Bend National Park last week at looked out over the Rio Grande at a number of viewpoints. It really isn’t necessary to have thousands of people patrolling the river. The area inland is very wide open and very inhospitable. I think it would be very difficult for large groups of illegals to escape detection. We did pass through one checkpoint about thirty miles or so north of the park. On a trip to the southwest two years ago, we noticed a lot more border patrols around southern Arizona.
Above Big Bend and below Del Rio, not so much.