There are only two solutions to this. Let it naturally fizzle out or get more boots on the ground. I've discussed this before in this thread, tear gas, plastic round and water cannon won't help. Not one person here has said that it will.
People who have experienced the use of these things say that it won't work either.
Stop being so naive and thinking shooting a couple of plastic rounds into a crowd, getting a few people wet and irritating some eyes is going to do anything other than antagonise the crowd.