My 9 week old GSD puppy tries to eat his own faeces, when he is stopped and I clean it up he will start biting my hands and arms like it's a big game but he gets into a frenzy and gets really aggressive and hurts. How can I stop him with both issues?
I stay calm, have tried 'yelping' at him, but nothing seems to work!

Oh good! I saw the title and was worried it was an adult dog... a puppy we can fix no problems.

I would try a water bottle. When he goes to eat it give him a good squirt in the face with cold water. It doesn't hurt them, but they don't like it and you can give them a form of punishment without actually touching them.

A lot of puppies eat their own poop and they do eventually grow out of it.
When one of my dogs was a pup he would actually play with his and bring it in and put it on my lap (YUK!) he is now over a year old and has no interest in poop.

Puppies and dogs eat their own poop for a number of reasons, lack of nutrition, boredom/curiosity, parasites or worms, or just to clean up their mess. Most puppies do grow out of it, but seeing as he is aggressive when you try to clean it up, it's time to take action. Shazzy made a good suggestion with the water bottle, another option would to put him on a lead while you are cleaning up the mess.

If he is aggressive in other scenarios, say NO in a firm voice, and walk away from him, you are showing that his un-wanted behavior is not getting him the attention he is looking for. If he doesn't listen to your NO when you are cleaning up the poop, then remove him from the situation by putting him inside, or cleaning it up as soon as he has made the mess. After all, the absolute best way to deal with aggressive behavior, is to prevent it in the first place!

Make sure you offer an alternative, preferred response to the action so he can be rewarded for performing it. For example, if you say NO when your dog barks, ensure that you give your dog a treat or lots of attention when he stays quiet, otherwise he will never get the proper message.

Set rules that are humane but consistently enforced. Get your puppy accustomed to you handling his food, toys, and his body. Let him know that toys are a treat, not a privilege, and that food is always served on YOUR schedule, not his. Additionally, cuddle and pet your puppy when he or she is calm, not excited. Do not work your puppy into a fluster and then expect him to not show his teeth or some snarling when you unexpectedly pick him up.

Finally, do not encourage your puppy's aggressive behavior with games like wrestling or tug of war. Games that encourage winning bring out the most aggressive behavior in dogs, so avoid these types of games. Instead, encourage light, non-competitive games such as running and playing fetch.

Thank-you, will definitely give the water bottle a try! Will post results.