So you've decided to add politics. Let's tack in another direction and look at what you have said, though: Your statement makes it look like you think Trump's wall has been built and other walls, too. You can't have "They KEEP BUILDING" without building having happened and continuing. Of course, maybe there's no logical thinking going on here.

As for walls themselves, there is one nation where they have walls (there may be others): Israel. And I've heard that NOBODY gets past the walls. In terms of keeping out people who don't have a right to enter, walls do perfectly well, though it's necessary for the government to patrol them, too.