He's still just a baby and figuring out this strange world. There are a lot of happy positive ways to deal with the landshark phase. I strongly suggest reading the puppy sections of this forum especially Puppy BITING!!! Teaching Bite Inhibition
I know when I first brought my puppy home I was miserable and thought I was doing something wrong, nope it's a GSD thing. I wouldn't worry about the whole "dominance, pack leader" business, first concentrate on establishing a solid bond and the respect will follow.