One of the strangest bits of conventional wisdom in the media is that no fence along the Mexican border
could possibly work. These pronouncements are often made by people who have paid a lot of extra money to live in gated communities.
Within America, there are countless miles of high-security fences and walls around prisons, nuclear power plants, armories, warehouses, factories, target ranges, airports and the like. All in all, it works quite well. This isn't nanotechnology. It's something we know how to do.
Similarly, the Israelis have found their fences around the Gaza Strip and the West Bank to be quite effective at keeping out suicide bombers, who are, by definition, highly motivated. Here's a diagram of the Israeli fence. The Israeli economy is about 1/200th of ours, but they've succeeded in effectively fencing off a border about 1/10th as long as ours with Mexico.