All dogs have some level of aggression. Different dogs all react in their own way, ranging from growling and barking to snapping or biting. From your dog´s perspective, aggressive behavior is a perfectly valid method of communication. Your job as owner is to communicate to your dog that aggression is NOT acceptable.
What are some of the reasons for your dog´s aggressive actions? Dog aggression is a complicated matter, but a common reason is a quest for dominance. Dogs are pack animals. One way that aggression manifests in your dog is in attempting to be in charge of, well, everything.
With you
As with all puppy aggression, this needs to be nipped in the bud. No matter what size your dog is or how young is it, you need to establish that you are at the top of the pecking order, not the dog. Do not allow a young dog to snap or growl at anyone. It is not cute. It is a dangerous sign that your dog is getting aggressive over food or play. With puppies, discouraging them with a stern tone of voice usually works. In addition, you may wish to start training your dog to sit, to stay, and to wait to eat until you release him verbally.
With other animals in the house
Again, especially with several dogs, this is a pack order issue. If you are the leader of the pack and establish this, your dog will defer to you and not challenge other animals for the top dog spot -- it is already occupied. In some cases, the pecking order of humans on top may need to be firmly established.
With strange dogs
This can be an issue if another dog challenges your dog. Ideally, both dogs are leashed and can be curbed or distracted from this behavior. Do not interfere in a dog fight without proper training. You will get hurt.
Finally, dog bites are dangerous to you and your dog. In some communities, one bite is enough to doom a dog to removal and euthanasia. Teaching your dog to be obedient and non-aggressive can not only make life easier for you and your pet, but may even save its life.
