I went to the link. I don't believe the fence would have to be at that exact spot. Because they own all the land they could use the path of least resistance. Mexicans are risking their lives to cross inhospitable desert every day and many of them are dying. If the fence is built only on the easiest places to cross the border they will risk their lives to cross at the more difficult spots. The "toothpaste effect" has already been shown in areas, like San Diego, where fence has been built and in areas with increased spot enforcement. The point is that the entire border needs to be secured, not just the easier areas.