When your dog pees in the house, soak it up with newspaper and keep newspaper in enclosed plastic bag. Next time u take it for walks, take the plastic bag and place it at the spot you want it to pee. let GSD sniff it, and dont move from area till he does it. After peeing, praise the dog abundantly (offer a small treat if possible) It will learn to associate that it gets praise and treat if it pees outside house, then when the habit has developed u can stop the treat. Pls take it for pee sessions aftre dog has had lots of water to drink, and remeber to wash the pee area in the house with a good biological detergent.
happy training - regards - Mark