teach an old dog a new trick

Question
We have a 8yr. old female german shepherd we love dearly, that lives in the country. Little did we know isolation would make her so protective. She would bite strangers or any animal she comes in contact with. We had a grown rotweiler who used to have contact with her. She would bite him and he was submissive. After a while she left him alone, but this happened every time they were together. Other than the biting, this is the most awesome, smart, goes out of her way to please us, loving dog we have ever had. My question is is there any way I can train a new pup with her to retain some of her assets or will all this be lost when she passes. The pup would have more social contact to prevent biting.

Answer
I would start with a 7-8 week old puppy from a good breeder.  Breeders that want to hold on to puppies longer are disregarding the well know importance of puppies' 6-12 week period.  If they are exposed to positive experience with people and other dogs in that period, they won't be aggressive to or fearful of them.  the more, the better.  You do need to take great care to avoid any possibly sick dogs, since puppy shots often are useless at that time.  

I would also start working on a good obedience program from the puppies first day.  The key to most behavior problems is approaching things using the dog's natural instincts. Dogs see all the people and dogs in the household as a pack with each having their own rank in the pack and a top dog. Life is much easier if the 2 legged pack members outrank the 4 legged ones. You can learn to play the role of top dog by reading some books or going to a good obedience class. A good obedience class or book is about you being top dog, not about rewarding standard commands with a treat. Start at http://www.dogsbestfriend.com/ For more on being top dog, see http://www.dogbreedinfo.com./topdogrules.htm

You might try looking at older dogs too.  One of the best sources for dogs with a predictable personality is the rescue dogs. These are dogs that lost their home, but were taken into a foster home to be retrained as necessary and placed in the right home for them. You may find a rescue near you starting at http://www.akc.org/breeds/rescue.cfm The rescues charge a fee to help cover their expenses, but is much less than the price of a puppy plus all its medical expenses the first year.