Boston Terrier aggression

Question
Our Boston Terrier is 2 1/2 years. He is an indoor dog. He is friendly with all our family and neighbors. He has never socialized at the dog park. We take him but he will only stay at our side. My friend has a jack russell mix and this is the only dog our dog will play with. They will only play at our house, not at the dog park. We have noticed that our dog is becoming more aggressive on our walks at the house. He is pulling on the leash and growling at other dogs and people walking by. I'm afraid he is going to try to bite someone. We're not sure what to do. We pull him back and tell him "no" and he will submit by going down and putting his ears down. He obviously knows he did something wrong, but the next day will do the same this again. What else can we do to correct the aggressive behavior?

Answer
He may not like the dog park and may not be suited for it, too many dogs he does not know and he may prefer only dogs in his "pack" like the dog you mentioned.  You can correct this on-leash behavior through training, but in a different way than you're doing now, I would try some lessons or a class, trainer search: www.canineprofessionals.com