Quite like the idea of the Electric Fence! Not sure about the nails though (earlier post).
I've had a cat for years and though I had sorted out the problem of her messing in other yards by providing her with a dug area in the corner of the garden. She poos in there fine, but have since found she still pees everywhere (luckily in my garden still as I too don't want to see her in the neighbours gardens doing her business)!!. Have a feeling its something to do with a new TomCat next door and territory stuff and wotnot, but its back to the old kitty psycology book again.... oh hum!

For the original poster, I suggest the same - a good cat book or weblink! If you're fighting the enemy, it's best to know their name!

Glenys