the rice in the bottle trick didnt work for mine with regards to chasing the hoover, so I just shut her outside.
I was going to say you should refrain from playing with him, but you say you tried walking away and it doesnt work, so presumably he chases you? A friend of mine had a GSD who was the same and as much as I love dogs, I stopped visiting as he was a nightmare and they did nothing to stop him, and it got to the stage that they couldnt take him out as he turned aggressive towards anyone walking past him in the street.
How about putting on some gloves that have been sprayed in bitter bite which tastes revolting? You have got to be very very firm with him, I have never smacked my dogs, ever, but I have in the past with a border collie who was very naughty grabbed her round each side of the neck, stared in her eyes and shouted 'no' - he has to know you mean business and it is not a game.
To ensure he knows you are the leader of the pack I have heard that you should stand over your dog with their body between your legs, and your head facing the same way as them, and bring their front feet off the floor at least once a day, dont know if it works, but it was on one of those dog whispering programmes.