Yes, that's right - part of a fence between the U.S. and Mexico in 2000, designed to stop cars from driving into the U.S., and built by U.S. border officials, is actually in Mexico by some 2 meters (about 6 feet). Doesn't seem like much, but ask yourself: what you would do if your neighbor put up a fence six feet onto your property? How about six inches? That's what Mexico is doing - asking for the fence to come down.
I saw an episode of Bullshit, a Showtime series hosted by Penn and Teller, where they talked about immigration, and the new fence the U.S. plans to build along the U.S.-Mexico border. They hired some day laborers, headed out to the desert, and had them build a portion of the fence to spec. That evening, when they were done building the fence, the day laborers were asked to get past the fence as if they were illegally trying to enter the U.S., which they did. In a few minutes (something like three, if I remember correctly). To state it slightly differently:
The fence the U.S. plans to build to stop illegal Mexican immigration will slow down illegal immigration by roughly three minutes.
Hardly worth the billions we're going to spend, is it?