Sounds like a great idea, as long as the fence is concrete, 20 feet high above ground and 15 feet below ground, topped with razor wire, 10 feet wide so you can walk along the top, and with guard towers every few hundred yards.
Let's do the same up north, too. Canada is a favored entry point into North America for ME types.
Cost is no object, as the net savings from a program would make it pay for itself very quickly.
One of the proposals I've seen that I like is that they would use the freeway sound barrier walls. I think they are typically 20ft high concrete barriers. I like your reccomendation of making them at least 15 ft below ground. A free-fire zone on our side of the fence would probably be useful too.
None of this, of course, is going to happen because Bush doesn't want to do anything about illegal immigration. He just doesn't give a damn.