You can disconect the battery, which i wouldn't recommend. This means the engine is still spinning, and might still be drawing fuel, but it wont be using the fuel. This will either break something outright, or eventualy lock the engine, where you will be unable to turn it over. I would recommend that you put the car in Neutral, hold the brakes, and simply let the engine idle away the gas. Or you can do something to interrupt the flow of gas, IE put a really big clamp on the fuel line so that it runs out of fuel and stops spinning. NEVER YANK THE FUEL LINE OUT! you will get sprayed with gas as the pressure equalizes, and you will look really dumb at the ER when they ask how you messed up your eyes. Then get it to a mechanic as soon as possible, because that is going to be a really big electrical problem.