I live about 35 miles from the border, and cross it regularly. I find it more than a little amusing that anyone would think that a fence would stop someone who has already made up his mind to walk for at least 3 days across a desert full of cactus and rattlesnakes, with little or no water and food, in scorching heat, with no shade, guide, or even a pair of boots. In AZ, we find about 200 bodies per year of those that fail to make it. It is beyond absurd. Besides that, few actually walk from the border to Phoenix. They are usually driven through the border in a truck or van and dropped off on the other side, to fend for themselves against the elements. Then, of course there is the other half of them who come over on visa's and simply don't go back. Down in Nogales, a bus fell through the pavement of a street, because it caused a tunnel under the border to collapse. The fact that China built the world's largest wall, which failed, over 1,000 years ago does not discourage Trump or his fans either.
The whole thing is just a continuation of the movement to keep the (Irish), (blacks), (Italians), (Chinese), (Jews), (Muslims), (Latinos) out.