As the title says really. I don't know what is so interesting about my back garden but it seems all the neighbourhood cats like tk hang out in it and it's driving me up the wall, my garden is big, and I don't want to spread granules or anything all over it so I'm thinking of one of them high pitch frequency things but I can always hear them when I walk past other people's gardens so the last thing I want is to listen to it myself but I need to do something! Any advice?!