arizona knows

http://www.cnn.com/2007/US/12/22/immigrants.leave.ap/index.html

Great, someone finally figured out what works. Harass the employers. Nobody needs giant prison facilities in the desert or fences. Just a natural barrier created by having to have some legal status in the country in order to work.
Now all we have to do is get rid of the xenophobia that comes with immigration and we're all fine.