An aggressive pug may be showing resistance to training. If this is the case, it may be your dog needs a little extra boost or a change in training techniques. Remember, the breed is quite laid back and prefers to lounge on the couch. So, using treats and positive reinforcement versus negative reinforcement to promote training will benefit you.
If your pug continues to be resistant, you may need to call in professional help. Consider taking your pug to dog obedience school or having someone come to the house to train it.