I don't know about decoying muleys, but I did hear a story that the DOW, in an attempt to apprehend a moose poacher, put out a moose decoy to draw in a moose and additionally draw a shot from the poachers. 10 minutes after the decoy was set, the poachers shot it.
I just do the spot and stalk thing. I did have a 3x4 come on me as I was hunting another buck. I sprayed my feet with doe in heat and didnt think anything about it and just noticed the other coming up my trail and he was 10 yds from me with his head down. Scared the crap out of me and him when he seen me turn. LOL but other than that that is all I have tried and used.
After firestorm of 91 the muleys started coming in droves. I could usualy get well within 100 yards of most any of them but what I found out to be the best decoy was my 99 Dodge deisel truck. I could drive within 10 yards of them and even stop the truck and get out as long as I didn't seperate myself from the truck.
That would be very interesting if a decoy would work. Maybe I will try that during muzzleloader season, I'm usually not to worried about getting close enough to deer with my rifle out here in open sandhills but on the rivers where there is a little more cover to hide, it might work well to get a really close shot on a big old boy in the late rut.
The record books, that are put out by Boone & Crocket and Pope & Young and where I live is Henry Kelsey they are a great way to research a state or a province for big game. This does take some time but the knowledge it gives you, can be very valuable. Not all hunters have their trophies recorded, as where I live after the Hanson Buck became the new world record typical Whitetail, we saw a flood of hunters and now that has happened, some hunters are shying away from the record books but...