Behavior Issues!

Question
Hi, Please note:
**I have a Male German Shepherd, 2 years old. NOT FIXED!
**I have a Male Pug. 4 years old. NOT FIXED
**I have a FEMALE PUG. Less then 1 year old. IS FIXED!
>>Here is the situation.
Before we brought home the NEW Female Pug, the Male Pug and the Male GS got along GREAT! I really mean....GREAT! They played with each other all of the time. Best Buddies to say the least!
**Now.....Since we brought home the new Female Pug and even after we had the female spayed, we have notice a GREAT increase of aggression from the GS.
**The Shepherd is VERY aggressive toward out Male pug. Several time during the day, we have to keep yelling at him and scalding him for showing his teeth, etc. towards the Male pug. We are worried that he is going to hurt/attack the Male pug.
**The GS is very friendly towards the Female pug!
**When (anyone) now comes to the door. The GS acts like he wants to bite them. Even if he knows who it is. It doesn't matter!
**WE are very concerned about this CHANGE in behavior!
**To the best of our knowledge, we know he isn't sick in any way. We know he doesn't have anything like lyme disease.
>>What do you think is going on here besides the fact that the Male GS is just trying to be the Alpha Dog here?
>>Do you think is we NOW got him fixed, if this would make any difference? Or is it too late for that?

Please help!
Any suggestions would truly be appreciated!
Thanks!!  

Answer
I think the only chance to straighten this out is to neuter him, and perhaps the Pug too. The Pug maybe showing aggressive signs you don't know to look for such as a stiff legged posture, holding his head high, eye contact, etc.  You also need to show leadership too.  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. Start at http://www.dogsbestfriend.com/  For more on being top dog, see http://www.dogbreedinfo.com./topdogrules.htm  Apply them to all 3 dogs.