
How old is your gsd ? Does he have the run of the house
If so and is still young -i- would be keeping him in one area of the house and let cat have the rest. Start teaching leave to yur pup but most of time you need to make sure he is safe from the cat. It is usually dogs who come of worse when they are young. Make sure you cat has plenty of places it can be away from the pup usually nice high spots are best. It takes a while but most cats and dogs learn to find a compromise. I am sure others will be along soon for more advice