h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

basicly you need to look at it from a cats point of view
do you want to crap in your own garden and advertise to the local toms you are here on a reguler basis no you go and deficate as far away from your home as possible .
Most cats do this being at heart a solitary animal we on the other hand a social animal and not generly in the habit of beating up the competion so we do not need to cover our traces.

several methods can be adophted to deter fouling by cats one method being get a cat of your own, then he will chase of other cats not wanting to advertise there own domain.Along with what has already been mentioned planting special areas with specfic plants,dont forget to take into account prevailing wind conditions as it is a bit of a waste useing scented messages(pheremoneal smells)if most of the year it blowing into next doors garden,is it.

Orange or citrus peel is also good ,egg shells can be effective as well added bonus source of nutriment for soil,water has allready been covered these can be "fired up/tripped" by beam sensors very cheap and easy to by even get solar powered ones,another method is sound,after all we all are at our most vunerable at this time,"does being caught with your pants down give any indication of dangers"

I suggest a visit to your local cattery to tape a few sounds.

have fun then.

mwahhahaapost 42 dont tell lill