I could dig a tunnel under the Great Wall with a shovel in a couple days. Ever seen The Great Escape!
You don’t think we can detect tunnels when we actually try?
So why do we build fences around airports, military bases, nuclear plants, the WH, etc.?
Oh yeah?
Not if we put somethin’ real bad underneath the wall...
and have towers every 20 feet with guys with uzis in them...
and crocodiles in moats on either side of the wall...
bet THAT would keep ‘em from diggin’....