I dont believe that this dog is completely untrainable.

Question
My elder sister's German Shepherd is a puzzle, He is overly aggressive with dogs and people - only 8 people are guranteed safety in his presence, the people he was introduced to as a puppy (he is now 7yrs old). He will not be trained - he decides what he learns. Over the yrs my sister has managed to teach him how to sit. I had much better luck when I taught him how to pull a sledge - like a husky. Although I haven't done that with him for 5yrs he still remembers the commands and follows them - if we can teach him how to do another dogs work why can't we teach him to heel!?!

Answer
Hi, you might try switching the training devices you have used to train him.  With most collars, dogs are capable of pulling against them and so it is harder to teach them to heel.  You might give head halters a try.  I almost exculsively use Halti Head Halters to train all the dogs I train.  There is no muscles in the face that can be used for pulling, so the halter tends to guide the head which guides the body.  In essence, they can not pull so they have to heel.  When you first use a head halter, most dogs will throw a little fit as they are not use to something like that around their muzzle.  If you keep their attention with a treat when you are first trying out the halter, it makes it a lot easier.  There are instructions that come with the halters that explain how to do this.  The packaging tells you what types of breeds fit each size, but in my experience, I have found that to be inaccurate.  Most shepherds fit a size 2.  Don't worry, a dog is never too old to learn new things.  I am currently training a 9yr old Min Pin in basic obedience.  Hope this helps.