There are all different types of aggression and there are different ways to treat each. If your dog starts to show fearful aggression, your dog is on the defence. He/she may be feeling frightened, threatened or he/she may react like this when they are in pain. You will be able to if your dog is showing fearful aggression as opposed to dominant aggression because your dog will show his/her teeth, your dog will emit a low growl or snarl or even barks, your dog's ears will be back, your dog's hairs down his/her back will be standing on end, his/her whole body will be tense with his/her back legs ready for rapid movement, and his/her tail will be held down and rigid.
If your dog reacts like this or you come across a dog like this, the best way for you to react is you will need to face your dog with his/her fear at a safe distance, then reward your dog with a treat, e.g. a biscuit, when your dog behaves non-aggressively or punish your dog by ignoring him/her. Each session, move the object of your dogs aggression closer towards him/her. However, if the dog appears to be in pain, e.g. he/she has been involved in a car accident, the dog will be feeling especially vulnerable and if you don't know the dog as he/she may be even more aggressive towards you, move slowly and calmly using a soft, gentle voice to soothe the dog.
Call a vet as straight away as there may be serious damage done to the dog they will also be able to give you extra advice on how to approach the dog depending on the circumstances.
Dominant aggression generally occurs between two dogs than between a dog and a human. However, if it does occur between a dog and a human it can be serious. Through dogs eyes, there is a pecking order in every household and the dog could be trying to establish a place in the pecking order, like they would have do in a pack of dogs. If your dog can see his/herself at the top of the pack, it will become their aim to get there even if it means showing aggression towards every member of the family, but more often than not it will pick out individuals as children may not be seen as a big threat. And, strangely enough people outside your family may not present a threat, your dog may be perfectly friendly towards them.
Your dog may also start to urinate in your house to stake his/her claim positively. If a confrontation situation arises, your dog will try to anticipate your movements and then block them with his/her body. Try and look for tell-tale signs of dominance when your dog was a puppy or a young dog, if you notice any signs you should establish your own dominance by grabbing your dog's scruff and rolling your dog on his/her back, this is a submissive position.
If your dog is an adult before any domineering signs appear this could be much more difficult but your dog still relies on you to feed him/her. The people who are targeted by the dogs aggression should take control using food, e.g.if your dog is used to being rewarded with food use this as your upper hand.
Another technique is called conditioning submission, this is when your dog would normally act aggressive and you force a role reversal, e.g. if your dog wishes to be petted and starts showing you aggression in an attempt to make you pet him/her, ignore your dog for a few minutes, then when your dog has walked off call your dog back and then stroke your dog, this makes you the dominant party.
The stance of a dominating dog is different to that of a fearful dog. The dominating dog will challenge you, his/her tail will be held high, the dog will be looking straight at you, his/her ears will be pricked and his/her teeth will be baring.
However, if your dog has been showing aggression towards other dogs, even if you have a well trained dog in your presence he/she may wish to prove this to the other dog treat your dog the same as in the above situation and if the problem persists contact your vet for further advice.
Another type of aggression is protective aggression. This could be directed towards a person, their family or their home and can be triggered off by noises of someone approaching your house or close contact between a member of the family and a friend, your dog would class the friend as an outsider and may see your friend as a threat. If your dog is showing protective aggression you will notice your dog growling and barking. In the event of this situation, you should arrange a meeting between the person(s) your dog feels is threatening him/her and the head of the household should let the dog that the person is acceptable and they won't cause any harm to the family. The head of the household will probably be seen as the leader of the pack through your dog's eyes.