Look at this guise! Law to support military building the fence! (forgive lowly faggot if repeat)

“The Secretary of Defense may provide support for the counterdrug activities” for “Construction of roads and FENCES [emphasis added] and installation of lighting to block drug smuggling corridors across international boundaries of the United States.”

Sauce: https://www.law.cornell.edu/uscode/text/10/284 US Code 10(284)(b)(7)

Hat Tip: @TheRealRaNon