Weasel, I think you're on to something there. My guess is that there are fewer, ALOT fewer 'yotes hanging up when a good moving decoy is used! Like Shaun said in this thread defeating one more of an animal's senses is always a good thing. A few drops of red fox urine under/around the decoy would be killer because it shouldn't scare off any fox and can only enrage a coyote! It's hard for me to imagine a coyote seeing a moving (i.e. alive) furry decoy and smelling its' hated enemy (fox) and then just passing it by like nothing happened! Especially, when the decoy is letting out distress cries at the very same time! I believe that each sense of a critter that gets defeated only serves to sell the deal a little more. If you sell the WHOLE deal to the critter (any critter) by defeating ENOUGH of his senses, he'll come in with abandon (which is what some of the posters in this thread were referring to)!
Back in the 90's, there was an innovative coyote hunter from Minnesota who wrote about his use of a full body mounted red fox. Talk about an EXPENSIVE decoy! Anyways, in this Peterson's 'Hunting Magazine' article, he wrote about one of his hunts. He is hidden inside a woodline with his red fox mount about 25 yards or so out into the field. He's calling across the field which is approximately a couple hundred yards across using a rabbit distress mouth call. Two coyotes break out of the woodline on the far side of the field (a good 200+ yards away). He said that they spotted the sound and the decoy immediately and broke into a dead run! As it happened, he managed to get both 'yotes but had to do some very fancy shooting (clearly why he chose this incident to write his story around) to keep the second 'yote from destroying the mount! The first shot took the 1st dog clean but did not for one second deter the second. I remember the pic showing both 'yotes and a whole lot of snow so this wasn't a pair of spring dogs defending pups (they were male and female though). The writer said that they were absolutely fixed on destroying that red fox!
He didn't mention the use of red fox urine but clearly, such a smell could only help to COMPLETELY seal the deal!