As above, chain through wheel and around the axle if I'm not going to be around for a few days. When connected there's not much that's easy or not a pain to do except lock the coupling. My trailer has 3200# boat on it so it's not easy to move around when not hooked up.
When my trailer is sitting in the yard, I use a lock on the hitch latch, and a locking ball insert. I also chain the wheels to the axle. I figure 6 locks someone will move on the construction guy down the way who just leaves stuff in front of them without blocking you from getting them at the side moving by hand.
Chain through the A, wrapped around a tree and locked. Ball in the tounge with the shank cut off, locked there too. My old dry rotted wheels and tires that dont hold air mounted. Basically looms abandoned in my driveway.
1991 XJ: 35"s, 4:56s 5.5"LA lift, stretched, locked, skids, caged, high steer, spray paint. I think it was stock at one point.
<-1978 CJ5 parts - click on my classified
I considered a number of options (locking / removing the trailer tongue, removing a wheel, parking boot, etc). But I wanted something I could deploy easy and potentially use for something else. I settled on a 'Tulsa chain' (which is almost impossible to cut given the design / strength) and a Abus 20/80 Disk Padlock (disk padlocks are extremely hard to cut as well and this one also had the reputation of not being able to be picked. Like the others, looped ot through my rim and over the axle. Since then I have also used it to secure my generator as well as my motorcycle when traveling.
I picked up 10ft and that was a perfect size for me, any larger and the weight becomes a concern. I also got mine with the protective cover, not so much for the chain but for the holes in the room through which I attach it.