Walls do work. I have been on both sides of the (former) wall between east and west Germany. Not just in Berlin, but also along the border in the forest. There was near zero border leakage. Of course, they were more politically "committed." Worked for China for a couple hundred years as well. Worked at the Maginot Line for a few decades. Heck, works for me with my neighbors. Nothing wrong with blocking unwanted incursion and forcing people to go through legitimate border crossings
Don't forget Hadrian's wall up there in Scotland.... Chris
https://en.wikipedia.org/wiki/Hadrian's_Wall