Get a CO2 fire extinguisher and hang it next to the garage door. If your engine runs wild give it a shot of CO2 into the air intake and it will stop right away with no damage.

You will have protection from fire too. The reason for hanging it near the door is you never want the fire between you and the exit. If there is a little fire and you are trying to put it out you want the door at your back just in case it doesn't stay little.