There are a whole heap of super strong toys out there for the super chewer. The Goughnuts guaranteed indestructible dog toy even comes with a lifetime guarantee.
Thanks for your question, it sounds like your German Shepherd is giving his toys a real run for their money!
His voracious chewing is quite expected as this age - he's basically a teenager and up to the age of 8 months his toys were providing him with some relief from the pain of teething. Now his 42 adult teeth are in place and he just wants to play!
At the moment you're lucky that his sticking to toys and leaving your shoes and furniture alone but if his toys don't last the distance this may change! There are many super strong chew toys on the market specifically designed for large dogs and should last longer than 1 week! My recommendation would be to invest in a few good quality, durable toys and rotate them frequently so he doesn't get bored.