What is the best way to kill off a Leylandii tree, without cutting?

My neighbour has one of those awful trees that grow 3m every year and it is out of control. They wont do anything about it, so I'm forced to kill the thing off myself. What is the best way to do this? Bear in mind that power tools are out of the question, and any activity will be done during darkness hours. Oh, if you cant help - then dont. I'm not looking for any discussion about morality today, thanks.