Wheel shackles.
Hitch lock.
1-7 of these
8,9,10 can be easily broken with a hammer, the yellow one is particularly cheap and useless. The pin locks are easily defeated.
Remove the safety chains from the trailer.You can hook chains on the trailer and the truck, they do not need to be welded to one side.
Multiple safety precautions are only a deterrent, but better than just one.
Tow a junky trailer full of worthless junk and a thief will run.
5th wheeler, few will have a hitch.
Removable tongue.
LowJack or, Apple makes transmitters that can be put anywhere and tracked, about the size of a logo button worn on a shirt.
Leave your phone in the trailer, hidden and on and with tracking enabled.
