I had 5 quads stolen in about a 2 year period. Regular locks and chains barely slowed them down. They even cut down the 6 foot fence and went through my neighbors yard so I didn't hear anything. I finally found a lock and chain that you can't cut with bolt cutters. They're about 3/4" thick. Then I bought two wheel locks like this TWL100
One would probably be enough but I'm not taking chances. Believe it or not my insurance didn't get cancelled. Too bad they only pay what they say a used quad is worth and they won't pay for a new one. I talked to the guys at Lo-Jack and they said they wouldn't warranty their system if you had it installed in an ATV.