unwanted guest in compost bin

[Alison Adams]

A couple of days ago I noticed an old plastic pot down the back of the shed was all chewed around the edges and wondered about a rat - though the pot has been laid there for maybe a year so it could have been chewed anytime. I havent seen any other indication and no disturbance to the nearby compost dalek. What kind of signs might I look for to know if there is current activity ? Can rat/s be poisoned without harming cats, mice, hedgehogs ?