Several choices. While I'm in an urban environment, I'm not far from several areas in the vicinity. Assuming the zombies cannot swim, and die after too long in water, and animals are non-infectable, these would be perfect.
Item the first: Mt. Dandenong
Probably not such a good idea, but it's easily fortified and there is a maze there that would confuse the zombies. Mount Dandenong- it's about 25km from my house and easily reachable by plane.
Item the second: Fort Nepean/Fort Pearce, Point Nepean
Ideal. It's an old fort. The national park before it has huge amounts of unexploded land mines. The road leading to the fort is three metres wide with a sheer drop of 10m into the raging torrent that is Bass Strait. Lots of old foxholes that are still usable. Extensive underground tunnels. Easily sealed off from the outside world by destroying the narrow road.
Item the third: South Channel Fort, Port Phillip Bay
Good as a stopping point. Poor opportunities for farming.... Easily defensible.
Item the fourth: Swan Island, Geelong
Owned by the Department of Defence. Soldier's training facility. Manned at all times. Only way in is via a bridge or through shallow water.
Item the fifth: French Island, Western Port Bay
Only accessible by boat. Massive farming abilities.
-Cons: Poorly defensible. Very large island. Western port bay, although dangerous at times is also shallow.
There you go. I'm fairly handy with melee weaponry, and I'm skilled at farming. i've not fired a gun before, though.