To slow down trailer/boat thieves while we are on holidays, (don't need it at home since both are locked in a shed) we got a second towball, attached it to a plate, attached a chain to the plate that goes through the goose neck and then put a padlock on that.
Bolt cutters will of course cut the chain but given that most of the time our trailers are stored at the places where where are staying you really only need a deterrent so that a thief takes a quick look decides it's not a quick steal and gets out of sight or moves on before caught it works quite fine.
It's the same old story if someone wants it they will take it but if you can slow them down all the better, we don't even leave our fuel tanks in the boat when we are on holidays and the boat is parked over night. In reality our boat just isnt worth pinching when it's parked next to so many others who leave rods, reels, fuel, practically everything in un covered boats where ever they are.