Growling is a way for the dog to communicate any number of things including fear, anxiety, fear, insecurity or stress. It could also be purely territorial or used a warning along with a very distinctive and accompanying body language, such as ears up, hackles up and tail erect to signify an offensive stance or ears pulled back and a lowered tail to signify a defensive and fearful stature, but still a serious warning to stay away.
When a dog growls, it signifies that he/she is experiencing a problem. It primarily acts as a warning communicated, although the reasons naturally vary with each individual situation. Try to determine WHY your dog is growling BEFORE any aggression on the part of the animal ever takes place.
Appropriate and responsible leadership skills, making sure the dogs needs are adequately met, along with increased exercise for excess energy to be naturally and safely depleted, may be required. But in intensive instances, it’s always best to seek the help of a qualified trainer or behaviorist first.