I would build large detention camps in Texas, New Mexico, and Arizona, use the National Guard to round them up, seize a secured rail corridor into Mexico, and run trains 24/7 until they were all gone.
But that's just me.
Employer sanctions will work, also - so let's do that.
Our 'friends to the South' would just block the rail entry with troops. Do you think they would want these people causing trouble over there?
For those that say, fine, let them go at it, consider this: the refugee flood would dwarf the current flow of illegals. No, as has been postulated by different posters, Bush is playing a much larger-scale geo-strategic game.
With an expanded WoT against a nuclear Iran, we can't afford to have any problems on our southern border. So he's betting the long-term composition of our national culture/society against the very-real short-term threat of a nuclear attack.
Why he doesn't just come out and say this openly is beyond me. He might garner a little more support...