Begin aggressive targeting of illegals in certain parts of California, Texas, etc. Make the apprehension public and the implementation of the new policies known countrywide.
Implement a Prop-187-type system where a potential illegal has to show evidence that he or she belongs in the country, whenever showing up for any official service -- hospitals, police station, school enrollment, etc. Those who don't belong are politely but firmly detained and immediate deportion procedures are begun.
Change the law such that for first offenses, illegals are fined $1,000 with fine automatically suspended if they don't fight deportation. With second and third offenses, the fine increases dramatically and their property in the US is seized -- bank accounts, cars, furniture. Also, implement a mandatory sentencing for multiple offenders.
Enforce the laws for employers who hire illegals.
Pretty soon it won't be economical for illegals to come anymore and they will stop. Others will return home because it isn't worth it anymore.
One final change -- get ready to have all our vegetables and fruits imported from Mexico, or that the price in the US increases. Those of us who dislike illegal immigration intensely need to accept this fact.
"Potential illegal"? That would be you, pal.
"Papers please! Your papers are not in order. Come with me, bitte..."