Unless we increase enforcement and deportation, a fence will accomplish exactly nothing--they'll still be coming in and their number will continue increasing. The only thing is that the rate of increase will drop a little. You underevaluate the force of human ingenuity.
OTOH, with sufficient increase in enforcement and penalties against employment, we probably won't NEED the fence in the first place.
I have always thought that for at least CA the guest worker program would work as long as there was a part II. That being that if they did not have a guest worker card in their possession we could contact INS to deport them.
IMO, I think the only answer to this will come when we have a majority on the SCOTUS so they can overrule the CA courts