I wouldnt worry yet. I have an almost 4 year old yorkie and we got him a brother about a month ago. Our older dog is pretty shy but can snap! At first our oldest (Teddy) wouldnt even go near our new puppy (pippo). Every time i would throw a toy for Teddy, Pippo would want to play too! Teddy would just run away. If Teddy was alone and playing or chewing a bone and Pippo would try to take what he had. Teddy would show his teeth and even nip the air (never Pippo, thank goodness!). It has been about a month now and they have graduated to play WITH eachother!!!! I am sooo happy now! I was so scared we made a bad choice. What we did to make pippo and Teddy know that the other was nice and it was ok to play. We would sit on the ground holding Pippo and pet Pippo's head saying "niiiccceee, Pippo is nice". We did the same thing with Pippo so he wouldnt try to be mean too. When one or the other would hurt or be mean we would hold the one who was hurt or had been mean to and show that it is hurt (even if it wasnt at all!) Just to get the point across that that was not good, without having to yell all the time. I have heard that if the old dog is only being yelled at he/she will learn to dislike the new puppy I think that trying to tell the dogs that it is ok to play and to play nice is best. It has worked for us. Scold when appropriate, both of them. It is hard for the existing dog to understand that the puppy is there to stay and is their friend!! I hope I didnt babble too much!
