How deep would a fox dig down before it got bored of digging to get to the chickens? Apart from dogs and cats the fox would be the main worry at getting to my chickens. Anyway by all accounts mint helps keep rats and mice away so although not being an apt saying I was thinking of killing two birds with one stone, my thought was burying these troughs round the run and filling with mint as mint spreads. They'd be about 6 inch deep.