Try this

I use a hitch latch lock, coupler lock, padlock the safety chains and a heavy bicycle cable lock thru the wheel and spring. Roger in Moncton showed me the wheel lock the Princess Auto sells https://www.princessauto.com/en/detail/trailer-wheel-j-lock/A-p8584997e . Going to get one next time they're on sale.

I picked up one of the J locks from Princes Auto when it was on sale.... I would say the weakest point is the lock itself... it's pretty flimsy pressed metal and a quick search in another section found a sturdier version of the lock itself - MasterLock make some as do Gorilla Lock I believe.

I also have a longer shank lock that goes through the plates to lock the jack in place too.... wouldn't be that hard to cut with a good bolt cutter but I figure anything that slows them down and makes them rethink the time involved to go through all the locks can't be bad.

I've also see people using the very heavy-duty chains to lock motorcycles... Kryptonite make some... probably others. They're supposedly hard to cut with a bolt cutter so the lock itself becomes the weak spot.

If you happen to be in Princess Auto check their surplus section for a Coleman Silent Hitch Pin Lock.... similar to this https://www.ebay.com/itm/5-8-Locking-Silent-Hitch-Pin-for-2-Class-III-IV-Receivers/392171446400?epid=535987584&hash=item5b4f3d6080:g:08cAAOSweDdaxqaS they're usually on for about $20.00 and help stop the rattling of the hitch in the receiver.

Another option is GPS tracking devices.... small self-contained trackers that can be hidden yet show the location of the trailer. SpyTech sells some versions

If some low-life jerk wants to steal the trailer they will.... we can only slow them down and track the trailer as they drive it away.