The photo by itself would be insufficient to distinguish between a large number of species of rodents in Australia. However, if these are fence palings about 1 cm thick, the animal is too big for Mus musculus (House Mouse); and in this location, i.e. an urban area in Canberra; and position, i.e. climbing a fence; we can discount all the alternative species other than Rattus rattus, therefore I will confirm.