What they should do is put a tax on crime. Non violent crime you have to pay the county 10% of your take. Because of the higher expense to the city for crimes of violence their cut goes up to 25%. Crime goes up, it is money for the city. Crime goes down, they can say their plan worked.
The only way they can lose is if the criminals don't pay. And every crook in Chicago since Capone got convicted knows you have to pay your taxes.