Once they cross the Rio Grande they are in the USA. Enough
fence and floating devices may keep the flow down a bit.
Hell they have been coming to this country since Columbus
sailed the ocean blue in 1492. Hell the immigrants went to
Africa and brought thousands on ships, etc. to this country.
The USA had a Civil War in the mid 1800s to free the slaves.
Now the freed people rule a lot of what goes on now days.
Enjoy your three score an ten as best you can.
c’est la vie