The first thing that people think of when a dog is aggressive is vicious growling and barking. True, that is a telling sign, but there are also many other things that dogs can do with an aggressive behavior.
Try feeding your dog in his/her normal food dish. Get something a little long and put it down towards there bowl and into their food. If they growl or bite at the object, then you know your dog is too aggressive.
If your dog reacts in a negative way any time somebody gets close to its owner then you know that dog is a little too protective and may cause harm in the future to somebody who gets close enough to the owner.
It may be possible to train an overly aggressive dog to be calmer and loosen up a little bit. Socialization is a key factor at this. If your dog is aggressive with his food, then always be around the dog when they are eating and get a little closer every time you feed them.
The classic scolding for bad behavior and rewarding for good behavior may be the best thing to make your dog less aggressive. If this doesn’t work, then just know you have an aggressive dog on your hands and make sure they stay away from doing harm to others.