Aggression can be caused by many things, one of the major causes of aggression is pain and illness.
Before I book an appointment for a dog concerning aggressive behaviour they will need to see a vet first for a thorough examination. Please check your dogs food for e-numbers and colourings as these can contribute towards unwanted behaviours.
Aversive training methods can also contribute towards aggressive behaviour as dogs learn to associate the trigger with an unpleasant experience.
I recommend where possible that dogs are walked in a well fitting harness with a lead attachment at the front, (or front and back) rather than just a single attachment on the dogs back.