my mate had a dog that did the same trick when we was kids we would of only been around 15 at the time it was bouncing down with rain so we went to try a rock spot near my house. we was wet threw before we even got there anyway the dog marked so we let him go, we both sat there eyes wide open not wanting to miss the bolt, but the bolt never came nothing happened in fact not even a bark. I remember us both saying he must be deep in we cant even hear him baying, an hour and 20 mins later out came the dog we both ran over to him to see if it had been up to anything not a mark not a smell of fox o