One of my jobsites was right on the Rio Grande, just outside of Rio Grande City. It was an interesting experience.
BP showing up on the jobsite in the evenings chasing illegals was a somewhat regular occurrence. We loaded up a 20 yard haul off dumpster with backpacks, water bottles and lord knows what else from a washout that was on the jobsite property but not part of anything we were doing construction wise - had enough cover that it became a defacto stopping point for crossers. They left everything, finally had to take a day with several laborers to clean it up because the Owner was worried about everything washing off the property in a rain storm and we were tired of dealing with animals rooting through it. It was against company policy, but our intake pump station was about a mile away right on the river, I never went there unarmed. At the end of the project I was told (I had left the company by then) that the intake sensor at the river pump station had to be replaced several times because it was shot up - apparently those on the other side thought it was some kind of monitoring station. That was a $30k piece of equipment that was replaced at least twice.
When I lived in AZ, there was a big thread on AZshooting.com about the southern border there. A good chunk of the border in AZ is the Coronado NF. It is sparsely patrolled by BP, there are even signs out that warn visitors that it's not patrolled and you are on your own if you choose to enter. This is soverign US territory we are talking about. Several guys would go down there and post pictures of semi-permanent (we assumed) cartel campsites, complete with rape tents. BP didn't do anything about it even though locations were provided to them. I had a couple of run ins with groups of illegals out in the desert, luckily no coyotes with them and they just wanted to go on their way. It will pucker you up a bit when you are out and about and come around a sage brush head on into 10-15 illegals when you are miles from anywhere, gets the heartbeat up for sure.