Let them join and then tax the sh!t out of them. If they stay - that's money in the bank, if they go - bye bye.
I’ve thought for a long time about a tax on illegals. A nice Catch-22, but it will never even get considered. A $5,000/head yearly tax to help defray the cost to citizens and legal residents. I bet the IRS would be lots more effective than the INS in getting illegals to self-deport.