Well if the dog has no collar I'm going to go out on a limb and assume it also doesn't have a leash. Therefore we are left with belt. Now call me pessimistic I'm guessing the dog isn't wearing pants, and call me unprepared but I rarely carry a spare belt... So the 'no collar' advice basically boils down to take off your belt (Presumably no quick or easy task when Cujo is chomping on your frickin' face) and use that to strangle the dog.
Now despite all the obvious impracticalities this has an important added risk, say it doesn't work and you die under that dog? You have your pants down, and your belt round the dogs neck, furthermore I believe post death erections aren't uncommon, so the police turn up to examine cause of death: "Pants down? Check. Raging boner? Check. Belt wrapped round dog? Check.... Well this is clearly another classic case of kinky canine bondage rape gone wrong. You go get that carved on his tombstone deputy, I'll go tell his mum what a horrid little pervert she raised."