Posted: 25/09/2012 at 22:49
Wherever there is any exposed earth (usually freshly turned, but not necessarily) I stick short lengths of bamboo cane into them (the earth, not the cat ) and so they can't get in to dig.
I also found that pepper dust (from garden ctr) works well to deter, though you do have to apply after rain.
There is one cat in particular who is very brazen and she additionally needs the odd squirt of water from the hose to keep her at bay
I've also heard that you can buy animal deterrent sonic machines, from places like Robert Dyas, which work by emitting a very high frequency burst of waves that animals such as cats, dogs and foxes dislike, without causing them any harm - battery or main operated.
Luckily for me I never had to resort to this, as the cats have now gotten the message.