Many radios have an engine kill button. You set it up to travel -15% or so, so the servo travels BELOW the minimum position and closes the throttle.

If you don't have this feature and have analog trims, we set the idle speed with the throttle trim 1/2 to 3/4 way up so when you want to kill the engine, you pull the trim down.

If you have digital trims but no kill button, then put your finger over the exhaust. It loads the engine with fuel a bit, but it's safer than putting your finger over the carb. Sometimes you can pinch the fuel line too, but that depends on your setup.

Setting your throttle stick so the lowest position kills the throttle is probably asking for trouble.

Good luck!