Use game theory, says Smith College economist James D. Miller:
....Mexico receives huge remittances from its citizens unlawfully working in the U.S., so it's currently in Mexico's interest to promote illegal immigration. A well-designed guest worker program, however, could change this and turn Mexico into a U.S. immigration ally.
.... we should create a guest worker program under which the number of legal Mexican guest workers is based on the number of illegal Mexican immigrants in the U.S. For example, for every additional illegal Mexican immigrant who enters the U.S., the number of Mexican guest worker slots could be reduced by two. Under this plan, Mexico has an incentive to reduce illegal immigration into our country.
....the size of the guest worker program could be determined by hard data. Perhaps for every person the U.S. border agents catch illegally crossing the border, the number of Mexican guest workers could be reduced by three. Or maybe for every kilogram of cocaine police confiscate from smugglers crossing the U.S./Mexican border the number of guest workers could be reduced by ten. Under either approach, the Mexican government would have a strong incentive to reduce illegal border crossings.
We could sell the plan to Mexico by making it seem as if we are rewarding good behavior, not punishing bad conduct. We would offer them a small number of guest worker positions and agree to increase the number if certain objective criteria were met. We could claim that only if these criteria are satisfied could we afford to allow in additional guest workers.