Those drop-bears can be killers for sure. I keep a croc close by just incase they do come down from the trees.
I've just ordered a TK41 for this reason. It's only 800 lumens but hopefully that weak output will be able to cut it. I don't have the Koala problem at the moment, mine is more so a Bandicoot problem. You know how it is, walk out in your backyard late at night and if you come across one and you look at those bandi's the wrong way and they'll bite chunks out of you. Same goes for Sugar Gliders, if they're not sucking nectar they'll land on you and suck your blood.
A big buck Kangaroo also beat up my neighbor when he took the rubbish out last week.
Cheers