Rescue dog biting

We got a rescue dog 5 days ago and he is about 5/6 years old. He is so lovely when he wants to be, but when he has something in his mouth eg a toy or a bone, he snaps like he is going to bite me or anyone else. He also does it randomly but not all the time I no we have only had him a few days and we don't no what has happened to him before. There are no kids in the house but some time we do have them visiting and we just want it to stop before he does bit someone. What can we do to make him stop?
Asked Nov 05, 2014

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