Tough employer sanctions, enforce them and most illegal aliens will go home as their income disappears
Biggest problem with that is that, despite the tyson's and obvious sweat shop industries, most illegals find jobs in four or five person shops where law enforcement simply is not concerned. They are body and fender men, small grocery clerks (where spanish is a requirement), (yes) gardeners & yard cleaners. They find jobs among legal immigrants and for legal immigrants or where they can work in the back shop and out of public view.
Just as we've always said that it is the small business owner who drives the economy at large, it is the small business owner who facilitates most of the illegal sub-culture within our borders.