Went to Big Bend National Park for vacation around 2002. Stayed outside of Terlingua. People crossed from Mexico to the US daily by simply wading across the Rio Grande. At that time it was very shallow at that point. Don't know what it is like now. In Big Bend you could walk down to the Rio Grande and pay a Mexican to row you across in a little boat, seemed a little deeper there, and on the other side was the town of Boquilles. Wonder if you can still do that.
first thing i thought of was concrete…