One of the most efficient ways to kill rabbits is by using a box trap set into the ground on a fence. It has to be a netting fence and one through which the rabbits are already passing, though.
The box is set in a hole directly below the fence, and has a run through which the rabbits travel from one side of the fence to the other. The floor of the run can be fixed in place so that the rabbit pass unimpeded till they get used to it. Then, the floor of the run is unclipped which allows it to drop when a rabbit uses the route. The rabbits drop into the holding box and can be accessed for harvesting by simple removal of a lid.
A friend of mine installed several of these traps and killed hundreds of rabbits with them. They can be used or disabled according to the population/problem and, being galvanised metal, will last for a long time.
Google 'Rabbit box traps' and be amazed.