Aggressive dogs are difficult to address in a generalised sense, as often the cause of aggressive behaviour is specific to the individual dog.
Power struggle
It is important that your dog realises it's place in your pack (your family group) is as the least dominant member. This doesn't mean it isn't loved and adored but when your dog is told to do something it should, if you take your dog's toy away it should not fight you for it, if you go near your dog's food bowl or bed it should not growl or protect it. If any of these instances cause aggressive outbursts; snarling, growling, antagonistic barking, there may be a power struggle that your dog is attempting to win. If your dog feels unsure of it's place in the pack because of mixed messages e.g. you don't let your dog do something but your partner does, it may become over-protective of something in an attempt to feel in control.
Dog bed
A dog bed should promote feelings of safety and comfort for the dog. This does not mean you shouldn't be able to go near the dog bed, but it should be associated with nice things always. Treat, pet and fuss your dog in its bed from the start so it becomes a happy place where nice things happen.
Rescue dogs
Often dogs from re-homing shelters have had nasty experiences with people. Although your new dog needs the rules set down from the start, it is important to be extra patient and encouraging with him. Use lots of positive reinforcement and learn to respect your new pet's personal space. If your dog will shy away from something, don't force the experience, wait for your dog to show it's ready to accept it. This will minimise the risk of aggressive outbursts from you dog, provoked by fear of a situation that is new to him.
