my 3 yo golden retriever and my 4 year old papillion has liters 6 days apart. the pups were all raised together without a problem. I still have 4 of the pap pups and 2 of the goldens mixed breed pups. Now after 18 months of cohabitation my golden has singled out the line femail papillion pup and become agressive. I had been out and upon my return all dogs were barking and happy tails wagging . next thing I hear is a yelp ..no snarling or growling. When I found them the female pap pup was badly injured. After emergency surgery for abd wall tear with herniation, pneumothorax and bruised kidneys along with 2 skin tears thing were going well. Five weeks later I saw the golden go at her again, thankfully I was close by so no major damage but 2 skin tears. I have the pap pup crated for a few days to let her heal but I am notiving that as soon as the dogs start barking ( due to someone coming into the house or nosies) the golden runs right to the crate and starts pacing. I have no idea how to handle this. Its not fair to keep crating one dog and I cannot possible keep constint watch. I would hate to have to rehome my golden. Any help would be greatly appreciated!