Offa could build a dike, China could build a great wall, but the USA cannot build a similar structure on the Mexican border.
I know. Isn’t it awful? My idea is much less expensive. Lay an anti-personnel mine every 4 feet. That’s about 2.1 million at $5 each plus another $5 to plant them. 20 million bucks to build a barrier. $2 million per year for 5 years to maintain it.
Sooner or later they’ll stop trying.