Another non-radio way of shutting it down, which I use on my car engines and several times on my planes, is to plug your exhaust. This causes the exhaust pressure to build up and choke the engine. If you choose to use this method, be careful, the muffler can/will get very hot, even with a properly tuned engine. Most of the time using this technique, I use my finger, but if the exhaust is either too hot, or it takes to long to kill the motor, put my finger in a rag if I have one handy.