but if you tell me how they hook up, I can help......
If its by pins, you can drill a hole through the end of the pin that sticks through a put a padlock on it, same thing when its off.
I don't see why you would lock it onto the truck though, they would have to steal the truck to steal the plow, right? When the plow is off, keep something parked in front of it so no one can just go hook up to it.
I always did think that the introduction of all the quick mount plow's a few years ago would result in a lot more theft, not sure if it did or not, just figured it would be easier to go hook up and drive off with one.
My Fishers all stay inside. I did build a setup for a guy though. I made ears similiar to the ones on the truck frame on a Fisher MM. I welded these together at the distance so they could sit in the plow frame. Drilled the pins for padlocks and then boxed it in so you cannot easily get to the locks to cut. I will have to find a pic. He leaves his out at his business. I don't know if it works or not but the plow is still there.
I think of my plows as pretty secure, being locked ina building or in a yard with a locking gate. Only if someone wants to steal your plow they will. Locks will stop the guys with out bolt cutters, only if someone wants to steal something bad enough they will. All ya need is a truck with a boom, and ya can load up all the plows ya want.
No matter what plows or parts can be stolen. I am always worried about the pumps. Easy to remove one on any plow. On mine instead of the locks that end up ructing anyway I just weld the nut to the bolt or clip to the pin. I keep spares incase I need to torch one off and swap in a spare pump during a storm.
The problem is the The Ultra Mount has no pins. For now it sits on my drive way. I try to always park something in front of it, but I can not always do that. I was going to try and chain it to something but there is nothing to chain it to.
heres what I do in the summertime. I run a big chain around all the plows with one lock, I also run a second chain under the plows and lock it to where the metal feet go. I figure if someone wants to steal them they will, but after they cut the lock and hook up the plow they will have one more surprise. By the time they cut the lock or unhook the plow maybe they will get caught.
pehaps next to the drivway you could put an eye in some concrete at or just below grade and lock to that.
I have also seen people switch around the wires or use a different electrical plug. Only downfall here is that if there is a problem teasting and troubleshooting by a dealer can be difficult. Plus as Geoff said there are other ways to steal a plow.