It's great that everyone here is putting forward ideas on how to deal with the issue.
The situation with the kangaroos at Eden Hills was actually really distressing. I followed the story closely. In the beginning some of the locals holding vigil, would regularly find kangaroos that had several gunshot wounds (not the head) and who were left to die very slowly and in agony.
This is what I believe to be the biggest issue when it comes to killing kangaroos (btw the annual kangaroo 'cull' in Australia, is the largest land based slaughter in the world - involving millions of animals - read more about it here
http://www.animalsaustralia.org/issues/kangaroo_shooting.php) along with the fact that a lot of the killing is done purely for the commercial market (meat and skins) - not population control. The killing goes on in such remote locations that it's impossible to regulate, and even if shooters do kill a roo with one shot (which many don't) if that roo has a baby, *the law states* it can be swung against a tow bar to destroy its brain .....I mean ....really - that is beyond horrific!
I think (almost) all of us here agree that killing kangaroos is not the way to control the population - you'll never kill all of them, and if conditions are good numbers will quickly climb again...
What is needed is a long term solution that uses several different methods in conjunction with each other (imho!) ...
Like fertility control, natural and un-natural barriers to prevent them getting to certain areas, relocation where possible, and as Maggie suggested, limiting resources.
It's just a matter of the powers that be recognising that simply letting loose with guns is ineffective AND cruel. My ideas above above may take a lot of energy to implement, but if all done at the same time, I think they's be more effective in the long term ....
That was a long post ....but do you think that would work?
And then everyone would be happy!

Especially the kangaroos!
And lastly - MASSIVE kudos to the Australian Society for Kangaroos in holding that vigil for SO long. They have prevented so much cruelty and should be commended!