Oh that is scary...I once got an airedale from Rescue. My DD came home from school and she had a water bottle in hand. Dog walked backwards and growled. DH came home and he did the same thing.
That nite the dog was out of house. Did not want to take a chance.
The rescue told me that he was seen by a psychologist and was okay. Two days later she called to tell me than he will never go to another home. He sits in chair all day and you do not go near him.
So glad I did what was right and booted him out!