There is a EXTREMELY simple solution to this kind of behavior.   BAN any kind of PROTEST, planned or unplanned.  BAN any kind of GATHERING or whatever kind of semantics you want to call it.   If people want to Protest, call your local politicians, email them, but stay off the streets or private property etc.  

If this kind of behavior continues, I predict there will be someone shot, very soon. 

Read the Sign:     BAN THESE PROTESTS