Unless I'm misunderstanding, the OP's dog isn't biting unprovoked? It sounds like there are specific triggers and situations. Conflating the issue by lumping dogs who have specific problems with dogs who are unpredictable isn't really constructive IMO. We're not in Hypothetical Land, we're talking about a specific individual dog in a specific individual situation. I have and I do (mixes, anyway). And I honestly I do but I don't understand where you're coming from. A manageable dog who bites with specific, known triggers isn't automatically an "unstable" dog IMO. And although the dog in question hasn't been evaluated by a behaviorist, from the OP's description that's where this dog seems to be falling for me with the information I'm reading so far. Now whether the home is an environment where everyone understands the behavior and takes it seriously and is willing and able to commit to that management and training is where the question of responsibility comes in for me. And the answer to that question is what is going to be different for every person. What is responsible for the same exact dog in two different households might be very different.