Having avoided many arts of wildlife (and collected some) over my time, I can say, that a good loud air horn does a reasonable job of telling roos to get out faster. I found, that kangaroos "usually" make at least 2 final direction changes, when already on the road and in the lights. Best thing "in theory" is, once you realize that a collision is highly likely: dim the lights to low beam, blow the life out of the air horn, brake hard, staying straight until the last moment,in the middle of the road, leaving room to go either way, anticipate the roo to turn back the other way, follow your instinct after that... Most of the time you don't have time to do all the above, lol, but no harm practicing, when you're alone on the road out bush sometime in the middle of the night.