I don’t think that the dog should be put down for acting like an animal. I think what should happen is that one should figure out the cause of his biting; dogs (especially one who you said was usually a great member of the family) do not usually bite for no reason. He could have a medical issue that you all are unaware of; perhaps your son pet his stomach or something and maybe the dog has stomach issues. First, I would consult with a vet and/or a dog behaviorist. My dog has separation anxiety issues and has basically chewed up the entire house. We are looking into putting him into a crate when we are gone (though he’s been chewing that up as well), and also, I called the vet who redirected me to a behavioralist. We are currently getting in touch with her. I really think that at this point, it would be prudent to figure out why your dog is biting, and if it can be remedied. If not, I would consider putting him in a shelter. But I don’t think that putting down a dog who is considered a member of the family is a good idea; I feel like it should be the last resort.