
There are quite a few reasons for dog aggression but firstly you have to understand that aggression for a dog is just a natural instinct which helped them survive in the wild.
With a dog like Fig, who was a stray before he was at the shelter, these instincts come to the fore to enable them to survive and you have to work hard to get them to return to the place that we want these instincts to be (at the back of your dogs mind).
The same can be said for puppies they are new to the world and everything around them is new and strange. Their natural reaction to this is fear and the defense is aggression.
The most common reasons that your dog will display aggressive behavior are:
All of these behaviors can be worked on and resolved with some effort and a bit of patience.