I have tried a number of hitch pin locks. Most are garbage. One had a very cheap keylock that I could kick open with a paperclip. Another one I nearly used decided to go into "secure" mode and jammed up completely.
So far, there is just -one- hitch pin lock that seems to do the job well. A Strattec BOLT lock. It comes with no keys. Instead, if you have a Big Three vehicle, it will key the lock mechanism to your vehicle's key.
The reason why I actually go out of my way to tout it... is because it works well, is incredibly hard to pick, is an automotive lock with a shutter (and a rubber cap), so dirt doesn't get in, and the four ball bearings hold the lock onto the rest of the hitch pin quite securely. Nothing else like it. It isn't cheap, but for something that you buy once and keep with the vehicle... it is worth it.