Rats are terrible all right, though stoats are worse. There has been some success with new locally developed trap technologies. These ones use a CO2 cylinder to strike the rats or stoats, then reset themselves automatically. http://www.scoop.co.nz/stories/BU1402/S00802/unprecedented-0.... Much better if you're a city boy who doesn't really like dealing with traps and dead animals too much.

We use a bigger version to catch possums. Its hard to tell how many we catch though, as the feral pigs like to carry off and eat the dead ones. Its really a fascinating logistical problem trying to eradicate a broad spectrum of pests.