I may be a bit late but since you're afraid of the wildlife of your
killzone Australia, your Australian wildlife will fuck up them zombies until they create zombie dropbears, zombie dingos, zombie bears, zombie orangutangs, zombie koala bears, zombie kangaroos, zombie imported gorillas, zombie Tasmanian devils who migrated from Tasmania and Zombie Stingrays to patrol the waters. And zombie super sharks. All 20 species of them in your monster-infested waters.
And only the snakes were mentioned. Not any of the 1028 specimens that are ready to fuck your shit up.
If you went up north you would be pretty safe. You could destroy the bridges then the zombies would have to cross waterways to get to you. Crocs would easily be able to take out zombies who stray into the water. Of course then you have to worry about crocs but which is worse, zombies or crocs?