It sounds like your ferret needs some serious supervision during his "out" times. His biting is definately a problem. Are there things in your home to distract his attention from the other animals? Could you set up a play room for your ferret? Giving him a room where you can close the door and let him play? I've got all that set up in our bedroom, complete with tunnels, toys and a rice box to dig in. That way my dog doesn't get too stressed and the ferrets get their out time.