Others say that fencing ourselves out of the Rio Grande does little good as well. Unless you're keen to just give up sovereignty to Mexico for a fence that won't work, of course.
Have the folks who are screaming about the fence seen how the Rio Grande River travels along the US-Mexican borders? The river runs almost across the entire borders of Texas and Mexico and it is shared by both the US and Mexico. There is no way we can build a wall on this river without a significant impact on the use of the river by the US or by Mexico. Only technical and human monitoring of illegal aliens would work on the borders between the US and Mexico along the Rio Grande River.
People can simple search the internet for Rio Grande River and Texas-Mexcio borders to see that simple fact I mentioned above.