Can't someone watch him while he's outside to make sure he's not working his way under the fence? Or if he's outside for too long to keep an eye on, in addition to the wolf scent could you get one of those sliding tree trolley things for him? (You know those things that tie on two trees like 50 ft apart with a leash on wheels attached to it...sorry not the best description ha.) That would at least keep him in your yard behind the fence. Also, if he isn't neutered look into that. Neutered dogs are less likely to want to roam. Even without the coyote danger it's sketchy for him to keep wandering off. I worked in an animal hospital for years and the hit by car dogs and the dogs who ate things they shouldn't (antifreeze leaking from cars etc) were always some of the saddest, especially since they could have been prevented had the owner kept them in the yard/on a leash/in the house. Not saying you don't treat the dogs well, just that it would probably be best to really work on keeping him from escaping!