||01-08-2013 02:21 PM
Based on when he does it (you say when he's playing or when you come home, which are both very fun, exciting times for a dog), I suspect it is a play behavior that is out of control.
I think you do need a trainer's help. Puppy class is great for basic manners, but training your dog is a lifelong process and when he develops an unwanted and potentially dangerous behavior like this, it's a good sign that you guys need a tune-up. Can you call the trainer who taught your puppy class about this?
How much exercise does he get every day? I agree with onyx'girl that often aggressive play behaviors like this pop up when the dog isn't getting enough stimulation. A tired dog is a good dog, and all the toys and chews in the world aren't going to tire out a puppy without humans or other dogs to help.
I also agree with Nothing in Life is Free training, and not tolerating this behavior. The second he gets amped up enough to attack, he needs to be shut down. In the absence of professional help, I would recommend a time-out or similar deprivation-based correction, rather than a physical punishment. With dogs who are already biting, there's too much potential for it to escalate into serious aggression if you use physical punishments without knowing exactly what you're doing.
But really, working in-person with a good local trainer is going to be your best bet here, IMO.