My 8 year old GSD has never had this problem, but her lab-mix son has. I gave her son to my grandparents as a present. He was going to be an outside dog. Sweet boy, lazy at times, hated walks but loved to cuddle. But then he started climbing over the fence and when we made the fence higher, he dug under the fence to get out. We finally just let him stay out since we were living in the country and he was fine, never hurt another dog or run off. I know you can't do that to your dog but I'd advise making the fence taller and/or training her to stay within the fence. Tell her it is bad to go outside without you and she should catch on quickly. I taught my 8 year old GSD to stay whenever I had to walk off somewhere without her. If all else fails, I'd install an electric fence for just awhile until she learns that if she passes that line, she will have consequences. Sorry if that seems a little harsh, its just, a little shock like that is better than her possibly running out into the road and getting ran over. Better safe than sorry. Hope she learns to stay put!