Hiya,My front garden is all covered with purply-grey slate chippings, and I certainly don't get any cats digging this up. When I was unable to get a matching colour for an adjacent bed, I bought from B&Q some chopped up old tyres. These are the same colour, look like slate chips, but are of course much lighter weight. It stated on the bag that it repels cats. This isn't exactly true, as our neighbours'one likes to sleep under my conifers in the shade ontop of these chippings. However, there is no digging or pooing going on, so maybe they work after all!
I posted a message to another gardener who has trouble with foxes and said that you can buy lion poo on the internet from the zoo. This is a natural deterrant and might be worth a try.
Lastly, my mum always used to say that my Grandma swore by using dried holly leaves as an anti-cat mulch, as of course they would be uncomfortable to the moggies. As a girl-guide I remember that all holly trees keep a huge supply of old leaves underneath them, very useful for starting camp fires!
