Tesco do an animal repelant spray, I'm trying this and lots of pepper, and watering the garden regularly - they don't seem as keen on the wet soil as they do dry. I've been doing this for the last 2/3 weeks and there's been a marked lack of catsh!t. Hopefully after a while they'll be accustomed to using their new toilet, and forget about my garden. I just wish cat owners were a bit more responsible in training their cats to use litter trays, instead of filling my garden with stinking piles of crap for either me or my children to inadvertantly pick up. Such lovely animals.