An anxious dog may not necessarily be a dangerous dog, but a lot of canine aggression stems from fear and tension. Sometimes a dog's show of aggressive behaviors may be a brief reaction to something that spooks him. Sometimes he is just being protective. Whatever the reason, it is best to approach an aggressive dog cautiously.
Types of Aggression
A dog can become aggressive for a few reasons. She may attack or posture, for example, out of territoriality or protectiveness if she perceives that her turf or pack -- meaning you and the family -- are in danger. She may also become aggressive out of possessiveness, such as when you try to take her food away. Fear-reaction aggression may cause her to become aggressive when she feels she is in danger of being harmed.
Typically, a fearful dog will cower or run away, but if she feels cornered or threatened, she will likely become aggressive. She may not bare her teeth, but her body language will signal that she wants to back away. Let her; do not get closer. Fearful dogs often nip rapidly, but often don't display outward signs of aggression first. Turning your back on a fearful or cornered dog will usually cause her to run up behind you and nip.
Know the Signs
When a dog is ready to attack or fight, he may become still and rigid or lunge toward you. He will likely growl and bare his teeth and may bark in a deep, threatening tone. He also may snap at you without actually biting. If he does make contact, he may butt you with his snout or wrap his mouth around your foot and try to move you around. The more aggressive he gets, the more frequent and damaging his nipping and biting will get.
Many factors can lead to aggression in dogs, including breeding and upbringing. Inbreeding, for example, can generate emotionally unstable dogs. Similarly, some breeds, such as Doberman pinschers, are naturally protective and may show signs of aggression as puppies. An environment of excessive punishment or teasing can also lead to aggressive behavior, as can a lack of socialization -- the process of getting a dog used to being around other dogs, people and places. Isolation from people or other animals may cause him to fear the unknown and react aggressively.