Fact is, the fence does work now. That is why they go around it.
Strange you claim a fence will not stop 100%, therefore it's impractical, BUT the Incentive Removal plan is 100% foolproof.
Do you have any incentive to enter Mexico illegally?
I'd guess not, which is why it's not a problem for the Mexicans.
A fence isn't keeping you out. It seems like the lack of incentive is pretty darn close to 100% effective.