Well I use a killer bee switch on my 1/5 scale two-stroke gas engine acts same as kill-switch; I use a 4 ch traxxas radio.
This alot cheaper than hitting a solid object, or a person.
But won't work on a glow engine; you might check what the Freeflight people for a shut-off on there timed engine runs.
They use a fuel shut-off device of some kind that used to a mechanical device, but maybe there's a newer electronic one.