If you're tired of reading political, sociological, and financial rhetoric about the Southern Boarder Wall, take a look at this article from the Smithsonian. I won't try to summarize it because it's too long and well written. It explains the process and problems building an 18 inch wide, 20 to 50 foot high rock/concrete wall a 1000 miles long on sand, loose dirt above bedrock 100 to 1000 feet below the surface.
What Geology Has to Say About Building a 1,000-Mile Border Wall | Science | Smithsonian
What Geology Has to Say About Building a 1,000-Mile Border Wall | Science | Smithsonian