Walls work for private property.
They do not work for the purpose of keeping folks from one country out of another country. Anyone who doubts this fact should check with China, or the former Soviet Union, or the current state of Israel. Not only can it not be done, 100% of all attempts are complete failures. It’s especially silly for this country to do it, since well over 50% of all illegal immigrants to this country don’t arrive over our southern border anyhow: they come here by plane and overstay their visas.
I am not one who wants to reduce illegal immigration (as I believe it is a net benefit for us), but if you do, there are ways to do it and none of them involve a wall. One way is to penalize employers who hire them. Another, much more lasting solution, is to help the countries with dire economic and social problems that create these people in the first place. A third way is to tank our economy: if we have a severe depression here be assured they won’t come.