In the last six months we have all seen a number of major incidents in US cities with fires, looting and injury caused by rioters. Standard procedures so far to quell riots include an array of 'non-lethal' munitions, tear-gas, and so on. Due to the unruliness of the crowd there is still an opportunity for both rioters, police, and DHS personnel to be injured.
I happened to be stationed in Berlin during heavy rioting, while serving with an Air Force unit at Tempelhof airport. I noticed that the local police simply blocked off side streets with vans (paddy wagons) and then approached the main group of rioters on the Kuferstendam (main avenue) from both ends ... with water cannon.
My suggestion is simple. Whenever there is a building or area to protect: set up a perimeter with portable barricades and place a fire engine and security personnel within the perimeter. Fire hydrants are typically located near any major building or courthouse. Every city maintains a fire department. When an order to disperse is ignored, focused high-pressure water will cool things down pretty quickly. And..... without using non-lethal munitions, flares, tear gas, etc. Also, with no harm to either 'peaceful protesters', rioters, or your own personnel. No one likes to get wet or be blown down the street with a hose. The only damage: a few bruised egos. A side benefit: very little worry about people starting any fires as you will have the tools in hand to stop a fire immediately.