over the years doing numerous short scenic flights at various shows and events, I have had a few things thrown at the helicopter - scoccer balls, PVC piping, drinking glasses, rocks, sober people running out to abuse the pilot. In my opinion the safest option it to remove the cause of it all - the helicopter with moving rotors! how can it be unsafe to remove the running helicopter? in my experience, people that are angry often dont think rationally and they will be the one who gets hurt - who is resonsible then?? event coordinators? air craft owner/company? PIC?
i certianly dont want to be the pilot sitting at the controls when a mad person comes up and looses an arm or gets decapitated!