To handle aggressive dog behavior, establish yourself as the pack leader, and make sure your dog gets plenty of exercise. Stay consistent in your training methods, and avoid any triggers or targets that feed into the dog's aggressive behavior.
Many cases of dog aggression stem partly from a lack of exercise. Daily, rigorous exercise is important for dogs, especially large ones, because it helps to clear their minds and get excess energy out in a healthy way. If an aggressive dog does not get enough exercise, this energy is likely to come out in negative ways, such as biting, snarling or growling.
Aggressive dogs need a style of leadership from their owners that is both calm and assertive. Since dogs are pack animals by nature, you must make yourself known as the pack leader, honoring your animal's instinct to follow a leader. Set clear-cut rules and boundaries in place for the dog, so the dog learns to trust and respect you.
In addition, dogs can lapse back into aggressive behaviors when pet owners regress to their old behaviors. Maintain a calm but assertive attitude with the dog, always enforce the rules, and never fail to administer consequences when the rules aren't followed.
If a dog is very aggressive, take it to a professional behavior expert. An expert can make sure you're implementing behavioral modification techniques correctly and help you create a personalized behavior plan for your dog.