aggression with an older dog

I have three dogs, all male. Two are Bearded Collies and our most recent addition (two years ago) a Jack Russell. The Jack Russell has adapted very well to our family with one exception. Our fourteen year old Beardie with hip displasia is at frequent risk of being attacked from behind by the terrior. The Beardie in his youth was the alpha of our dogs, but now is a mellow elder, gentle and totally non aggressive. Why do you suppose he is the target of this aggression and is there any way to discourage it?

• Re: aggression with an older dog May 29 (0)