While our immigrant-hating President seems to be torn between building a 35-foot-high concrete wall or a 35-foot-high steel wall, author/historian/Dartmouth professor Pamela Kyle Crossley has written an article for ForeignPolicy.com explaining why neither option will be effective. She points out, among other things, that "people can now fly" and the United States has "two long coasts."
Walls don't work
https://foreignpolicy.com/2019/01/03/walls-dont-work/