I'd like to think, though I'd probably be wrong, that nobody will [bleep] with my ATV when I leave it somewhere and continue on foot. Of course I'll try and park it out of sight, but eventually some stupid [bleep] will come across it with bad intentions.

There's no steering lock like a motorcycle. There's nothing to keep them from putting it in neutral and rolling it off - whether that's toward their truck or off a cliff just to laugh.

What do you use to try and keep it somewhat secure?

Does it have spoked wheels? If so, you can carry a chain to run through 2 of them.

Around 50 years ago while I was attending the Colorado School of trades (gunsmith division) one of our instructors told us his father and three friends had hiked way back into an area to hunt Elk. After they go there they heard a noise and here came two hunters on honda trail bikes. They were really upset as they had quietly hiked in to not spook any Elk that might be in the area and now came these two lazy jokers on their bikes. Later that afternoon one of the bikers asked them if they had seen their bikes as they must have forgotten where they parked them and they couldn't be found. They never did find them but we always suspected there was more to the story than they told.