Wild rabbits as pest destroying farms?
I recently read a news about this at
http://www.abc.net.au/news/2012-02-21/calicivirus-resistant-rabbits-causing-havoc/3843098
edit: another news about pests
http://www.abc.net.au/news/2012-05-16/poison-baits-trials-feral-cats-pests/4015082

Or maybe the cane toads too?

Can pests be prevented organically and naturally without biological control like virus or something
Like maybe building fences around?
Hmm.. something to research and try later..