Buy an Optical Kill switch from 42Percent products. It works great and is very easy to install and use. Most folks connect it to the gear channel on the Rx. Nice thing about it is that it is optically isolated and it is very reasonably priced. Connect it in series after your regular heavy duty manual switch and before the engine ignition moduleso that for the enging to run you have to have both of them turned on. Said another way, start at the battery, then go to the manual switch, then the Optical Kill switch, then the ignition.

Hope this helps.