I was lucky enough to be on one of our pest free island when the only resident rat was caught. The effort and expertise of the rangers was truely amazing. They knew the rats favourite foods (a particular brand of peanut butter) and habits (avoided traps, went through monitoring stations). They tracked it over several days with cameras and monitoring stations.
They customised a monitoring station and killed the rat with a trap in the middle of it. The crack killer team spend their time tracking down and killing hard-to-get pests in truely remote locations like Little Barrier Island. https://i.stuff.co.nz/environment/100925042/eraticated-roden...