Sure there will be some problem areas such as recalcitrant landowners — just build around them and patrol for now.
I just found this. But from maps I’ve
of existing barriers on the border,
some are set back quite a ways from the
Rio Grande.
From the WIKI...
The Roosevelt Reservation is a 60-foot (18 m) strip of land on the United States side of the United States-Mexico Border under the jurisdiction of the United States Federal Government. It was established in a 1907 Presidential Proclamation (35 Stat. 2136) by Theodore Roosevelt in order to keep the land “free from obstruction as a protection against the smuggling of goods between the United States and Mexico”