I have an 8 yr old black lab mix who has been the only dog in the house for about 5 yrs or so. He has usually gotten along with other dogs and puppies in the past but that changed when we recently introduced a 6 wk old lab/terrier female into the home. It has been 4 wks since we brought her home and they were doing...ok... with a few knips and growls from the older dog but nothing major until this wkend when we were all in the living room and the older dog was getting agitated with the puppy (showing teeth) and before we knew what was happening the older dog lunged at the pup and punctured the back of her head and nicked her eye. Luckily, there wasn't any serious damage done, accept the $200 vet bill, but seriously, we thought it was much worse b/c there was a lot of blood. We brought the pup home and the older dog really acted weird, which I took as him realizing something really bad had happened. I didn't punish him for the incident and didn't scold him for showing aggressive behavior (showing teeth and a lil' growling) before this b/c of some advise a friend gave which was to just let them work it out and they would eventually get along. Sorry about the long story, but I could really use some help with trying to make them get along. I suppose I should punish the older dog if and when he displays this aggression twrds the pup? Any help would be appreciated.