Any lock will do. You don't really need the bolt proof kind. Trust me, if someone wants your trailer bad enough they'll get it. You can put a lock on the trailer but is your ball mount locked into the truck or just there with a pin? I have a lock on the pin too, but then they could just take the tongue off the trailer and replace it with their own. We had a theft ring from Canada a few years back that came down and took a bunch of bass trailers. Makes it a real B!+@#, HOW do you get your boat home?