First of all, that lady at the pet store obviously does NOT understand dog behavior. Just because your dog was barking at her dog does NOT mean that he is aggressive, some dogs are just barkers… it could mean SO many different things. What you need to look out for is his hackles up (hair along his spine) tail up or down… lowering of the head, cowering or growling. I think that obedience training is good for any dog because it gets them used to being around other dogs and other people. And it also helps you to recognize the signs in your dog that you need to be aware of. All dogs are different, and bulldogs tend to be a little more OCD than other breeds.