Reduce your speed before attempting to stop the Ripstik. Practice stopping intentionally so you are ready when you need to do it in a split second. Find an area that is free from obstacles or any loose gravel or dirt on the concrete. Do not attempt to learn to stop on a steep decline. Make sure the area is flat.
Slow the board down to a walking pace or just above a walking pace by simply letting the board ride without twisting for speed. To stop, simply step off the board and take a few steps to slow yourself down. The board can not balance on its own, so it will not roll off on its own. Make sure to keep moving as you hop off the Ripstik as you risk injury through falling if you forget this step.
Practice hopping off at higher speeds once you are comfortable executing this at low speeds. Jump off the board and into a slow jog or run if you are moving at that pace. There may be times when you are reacting to another skater or an unseen obstacle and need to be off the board instantly. Ready yourself for these moments by working on the technique of leaving the board at moderate speeds.