It only takes one time.
a truck was bouncing around my town(very suspiciously) and of course me and my friend being night owls were out dumpster diving behind the computer shops
needless to say few garages got broken into that night(not by us) and said truck has been seen in other towns, needless to say we decided to load my quad into the back of my truck the next night to lure them out to my house. i unloaded and decided to "go back into town" actually i just sat in my backyard and waited. not even five minutes and they popped into my yard and started snooping. after i made the call, they were surrounded by about 7 12gauge shotguns with the sheriffs department on the way. they were charged with intent to burgularize and holding stolen property.
not to mention a certain race that likes to steal diesel out of tractors and other ingredients to make some drugs were caught in other peoples yards.
In all honesty though, be smart like my dad, have your quad set up to start a certain way. IE: wire a needs to be connected to wire b before the engine will pop off. so basically on his tractor you can try to start it, but if you dont know about the wire or where it is, youll never get it started. i mean in the end they can still make off with your fuel and maybe handle bars, but thats more replaceable then a quad.