Surely there has to be a better solution then bringing him to the shelter! It sounds like he will be put to sleep, thats a horrible fate for such a beautiful dog that is clearly loved by you.
Is he neutered?
Have you tried a behaviorist?
GSDs can be territorial, but I do believe the vast majority of behavioral problems in dogs can be resolved.....with changes on the owner's part.
I hope for your sake, and your beloved dog- that he is not euthanized! Please keep us updated....and let us know if you need any help. I know of a few great GSD rescues that may be able to help. They might even be willing to speak to your mom.