Electrify them. Like big bug zappers...
The hell with these pre-genocidal revolutionaries.
Wanna stop this crap? And anyone caught burning the American Flag should himself be set on fire on the spot. Harsh measures prevent bad actions.
Fun idea... monuments with cattle grid decking around them for rioters to attempt to cross. It could be an entertaining reality show, we could bet on how long it takes for one of the rioters to try to urinate on it, and on how far he jumps or whether there will be smoke.