It rolls because it has a high center of gravity. You can reduce it by lowering the truck by making suspension adjustments, widening the stance and just plain learnng how to drive the truck.
The main ways to stop the engine are; Pinch the fuel line, block the exhaust, stop the flywheel, and block air flow to the carb. As to which is best, well that's pretty much a matter of debate and personal opinion. Some manufacturers reccomend pinching the fuel line, some stopping the flywheel and some blocking the exhaust. Very few reccomend blocking the carb. My preferd way is to block the exhaust but probably the best for the engine is to stop the flywheel. The only one that can be harmful is blocking the carb because of the possibility of getting dirt/debris in the carb.