Rent some warehouses, buy lots of concertina wire. If/when the riots start, surround the area, cut off routes of ingress / egress via concertina wire. Surround, contain, secure the area, then wait till the rioters surrender. Cart them off to a warehouse and secure them there until a judge sees them for processing.
An "accidental" warehouse explosion/fire might not be a bad thing...they would do it themselves and blame the Republicans.