My 2 year old black lab LOVES tennis balls. I've only had her for 3 months but her personality is pretty easy to see. We go to the dog parks frequently as I don't have a yard. She loves going there, but we tend to get into trouble most of the time we go. She will sometimes jump the 4' fence to go fetch foul balls. Most people don't mind, but I find myself giving the same speech to the other dog owners. When she stays inside the fence she'll be fine playing with me and our own ball, but as soon as another dog/ball/owner show up, she literally drops her ball and runs toward them. Then, she will only fetch for the other person and their ball. What's the deal with that? Sometimes she will take their ball and not give it back, which is the embarassing part. As much as I try to entice her to play with me and her own ball, I can't win her over. It's only when the other dogs leave that she will pay attention to me and our ball. Any advice to help me would be appreciated.