Within Australia the main laws relating to assitance dogs are governed by the Federal Disability Discrimination Act 1992, Section 9. This legislation overrides all other local, state and federal government legislation.
Dogs are classified into three types
Guide Dogs for the visually impaired
Hearing Dogs for the hearing impaired
Assistance Dog/Animal for other disabilities.
This legislation only overrides other dog legislation in such a way that people are allowed access with these dogs when they would not normally be allowed access and cannot be treated any differently because they are accompanied by a dog. If local or state laws require dogs to be on leads or otherwise tethered in some way then these laws must be followed.
Individuals are still legally responsible for any damage caused by their dogs.