I am of the opinion that what can be done to stop it is someone carrying a firearm for self defense, another with a video recorder, and then exercise one of the many freedoms that violate sharia law. When this extremist comes over an attempts to enforce Sharia, laugh at him and tell him to go away. When he gets enraged and assaults you, defend your life from the attack with aforementioned firearm.
It wont take too many of such situations to either remove the threat or get the word out to the muzzies.