Markuson
SILVER Star
I use a master lock on my hitch (like this Amazon.com: Master Lock 2866DATSC Swivel Head Receiver Lock, Chrome: Automotive) so that someone can't pop the $200 WD hitch off, and a separate long shackle master lock on the trailer coupler. The latter helps ensures the tongue doesn't pop loose when driving, and I lock it when I'm detached so someone can't steal my trailer. It's not like it's not insured, but I'd rather not have to replace my stuff too.
If I had a yeti and gas cans on the back of my truck I'd at least use a bicycle cable lock with it. When I eventually get a rear bumper I'll probably poll the group about how to secure the spare since occasionally there's a rash of spare tire theft in the city. Like Markuson I realize I won't stop a determined thief but I'm really just looking to make others more attractive targets than me.
I used a very thick bike cable to secure my spare on my old Slee swingout. It barely shows if you simply run it from the back...out and back in one section on the spare and secure behind. Keeps the look clean too. On my cans, I'll do the same thing just to keep them from walking away. Same with my mountain bike if it's on a hitch rack. Couple loops through each wheel and frame triangle and I'm free to hit the local breakfast shops on my way through sketchy towns.