IF THE DOG IS SHOWING AGGRESSION TOWARDS YOU OR A MEMBER OF YOUR HOUSEHOLD ...
... you need to see a Vet Behaviourist. Contact me for contacts within Australia or speak to your local Vet.
If a dog has suddenly changed personality or is getting progressively nastier and the behaviour is out of character, s/he may be in pain and should be checked first by either your Vet or the Vet Behaviourist. Please advise them and their staff that your dog is/has become aggressive so that they can be prepared. Thank you. : )
You can also have telephone consults with a Vet Behaviourist (usually around 15 minutes - you will be charged and rates vary) - they will not want to see the dog "in action" as that just gives the dog another chance to practice the behaviour! They can then advise you on a future course of action and/or whether you need to come in and see them. (FYI, put some time aside as some initial consultations may take up to 3 hours.)
Don't take unnecessary risks and delay in asking for help - contact a Vet Behaviourist.