x-posted in Aggression...really need advice.

First the basics...How old is the Pom?  Do you know his/her history?  What are you doing to "assert alpha?"  What kind of training have you done with this dog?  What kind of socialization?  Is this a recent onset?  Is there aggression at other times too?

Hi.
1. Two vets up to this point have said that they would put him between 4-6 and they are comfortable with him being around 5.
2. The only history we have is that he was in a high kill shelter in OH. Most of his teeth were removed and other then that he was intact and they think he may have been bred with.
3. We are feeding him last in line and not allowing him to go through the doors before us and not tug on the leash. I know that we need to work on me not dropping everything to pay him attention.
4. We are in an positive reinforcment class. *but he seems really scared of the big dogs there and really distracted..we have only gone once. We go again this thursday.
5. We go almost daily to the dog park..we have roommates and he goes most places with me. We don't have problems outside of the house.
6. The growling and bitting has come within the last few days. Mostly since the class honestly.
7. He doesn't have food aggression or anything like that..he just is super protective of me and mostly in the house.
Hope this helps.