GSD aggression

Question
I have a 15-month old male gsd.  The other night when I came home he barked when he heard me open the door.  When he got to the door,and saw me his hackles went up and he was barking ferociously.  I waited to see how long it would take before he recognized me, because at first I thought it was funny. Then it scared me because he truly didn't know it was me.  My other dog was standing near me wagging her tail, and yet my gsd never caught on that it was me.  Once he did, he was all kisses and wagging his tail.  Did I just spook him?  Should I have said his name right away?  
He's also been "herding" small dogs and biting them in the rump at the off leash park.  Is this normal?  I figured a simple recall would fix that, but it's still embarassing and he could hurt the other dog.

thank you

Answer
Yes, I would speak his name.  

You may want to obedience train him.  The key to most behavior problems is approaching things using the dog's natural instincts. Dogs see all the people and dogs in the household as a pack with each having their own rank in the pack and a top dog. Life is much easier if the 2 legged pack members outrank the 4 legged ones. You can learn to play the role of top dog by reading some books or going to a good obedience class. A good obedience class or book is about you being top dog, not about rewarding standard commands with a treat.