We had rats in our other house, when we arrived just before christmas
we had had them before they came in to the space under the cuboards the rat man had left some posion down from last time they are blue blocks that look like dishwasher tablets
anyway the poison had gone but so had loads of crisps and quavers from the cupboard and loads of poos and wee in its place
Anyway DH cleaned it all up and we got the rat man from the council to come back
and he left us with 18 blocks of poison
1 block kills 4 rats
anyway a couple of days later all blocks had gone
They come and collect the food and take it back to store it and when it is all gone they return
we laid rat traps with the spring over thingy {larger versions of mouse traps}
we had set them with peanut butter, but they still went for the poison blocks - which are cereal based
Rat man said they couldn't resist MARS BARS so DH went to buy MARS BARS for the rats but as they had already taken all the poison and had all the crisps stashed away they didn't live long enough for the MARS BARS
so we have left the traps set just incase we have any more while we are up here
THE ONLY THING THAT RATS CAN'T CHEW IS STEEL OR SOLID GLASS
Previously they chewed through concrete to get in
we were told they are neophobic and so don't like new things
good luck
IMHO get the council in they don't charge and our RAT man is lovely and very posh
BTW we have 2 cats who were shut in the kitchen overnight but the RATS still came in
as they didn't have access to the room just the space under the units the cats were safe
RATS are NOT frightened by cats and will love to eat their dry food btw - our cats just have tinned so weren't sharing with them
our cats do catch mice etc but we haven't had them for years