Something that we have used for years on our tires down here in texas is when you get a hole from say a mesquite thorn take a self sealing roofing screw that has the rubber washer on it and screw it in not the best in the world but will get you home. We also use the plugging kits like one of the guys above me stated and they work like a charm but you have to be sure to get the right kit for a pickup that takes 80psi because an atv plug will just blow out once you get above about 40psi. And something that my dad uses on his tractor tires when they are leaking is to put berrymans sealer in the tire and then give it a shot of propane it works every time. But for gashes that is the best idea i have heard in awhile.