So I have friends that foster small dogs. They currently have 4 ****zus of their own, 2 small foster dogs that have been with them for 3-4 weeks, and then Super. S came to them as a rescue and when they found out he was 17 years old, they decided to keep him. Hes been with them for several months now and all of the dogs get along and play together great, until about 3 days ago. Now all of a sudden the Super has developed aggression towards one specific ****zu and will seek him out to attack him on a regular basis. He's not aggressive at any other time or towards any other dog. Any thoughts or suggestions? They don't know what to do at this point.