Chester was together with my brother in laws 4 year old 125 pound German Shepherd this weekend. These boys could not get along. I have never seen Chester bare his teeth and growl like this before. He had that Shepherd running away from him. For a little bit they were okay if they stayed on their own sides of the yard but if the Shepherd would go toward my kids Chester was back on protection duty. The dogs hadn't seen each other in about a year. At the time Chester was a lot smaller and the Shepherd would nip at his back end. I wonder if Chester remembers that or if it is just a case of boys being boys. Any ideas?