aggressive chihuahua

Question
We have a year old male chihuahua, who after having a chow try to attack him in our yard, has become very aggressive. He was not before. We are having difficulty with barking and him pulling excessively on his leash(before we didn't need a leash on him, he would walk with me like our older chihuahua with no problem) He's getting worse, what in the world can we do to get him back to where he was.
Thank You

Answer
Neuter him if not already, and then obedience train him.  he 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