We have an 11 year old Rottweiler/Shepherd, female neutered dog. She has not been socialized well with other dogs and we cannot take her to the dog park because she will starts fights. We would like to get another dog, a small, male adult dog. Our attempts to introduce her to other dogs on neutral territory, unleashed have been unsuccessful. Is it possible to socialize a dog this old, or is she set in her ways? Should we hire a professional trainer? Any ideas would be appreciated.