I would say he needs way more exercise and you need to work with him, not against him.
Tail chasing is obsessive behavior(serious!)
Can you get him into some agility or herding type classes? It really isn't fair to him to ask him to settle with a peanutbutter filled kong or walks....those do not work his brain! Treibball would be a great way to work him!
He needs an outlet for his energy. GSD's are a working breed, they need to exercise both mind and body. It isn't his fault he is who he is, you need to step up and help him be the best dog he can be!