Pedigree German shepherd/ no papers

It is with great sadness that I have to rehome my German shepherd to a loving home, he has just turned 3 but I am no longer able to give him the exercise he needs, he is a big dog that can be aggressive to strangers, so I WILL NOT let him go to anyone who has children, or has no experience with breed, he is a brilliant house dog, that needs a new loving home , the money will be donated to the RSPCA, also I will NOT let him go to anyone, but only to a mature person with experience who is able to give him a loving home.