The last time I flew I overheard someone say they could not get their engine stopped. They obviously did not have their trim set so that all the way down would close the barrel. I landed and was thinking to myself, put your finger over the carb... But I watched in horror as the guy grabbed the spinner with his bare hand... I did not have enough time to shout at him, but it worked and he didn't get hurt - luckily. Even if I had a cowl and could not get the enging stopped I would tie her down or straddle her and keep her from moving and then just let the fuel run out. NEVER stop the engine by grabbing the spinner!