Go to the bottom of the water at the end of the island in Flint county. Enable the "Maximum lung capacity" code, then swim down to where you see two rocks and a large starfish. Swim behind the biggest rock. Sooner or later, you will be able to walk on the bottom of the ocean. You can spawn vehicles and fire weapons. Do not get out of the water or try to fly a plane or you will have to do this all over. Also, if you go too close to shore or out too far, you will respawn on the nearest island. This glitch may take a lot of time to do and requires patience.