I have a 3 year old Chihuahua that wants to held but when I put him down he will growl. If I make him get down, verbal and point for him to get down he will turn around and bite me if I don't get my hand back in time. He has bit me in the past. He has been to obedience class and did well. He has been fixed. I also have trouble with him marking all over the place. What can I do to help stop this? He is litter box trained and does great. I have two other Chihuahua's and he is the only one that bites. Can you help me?