The neighbours cat has never covered its mess and the neighbours are ones
that don't give a hoot. We have a ranch fence down
both sides of the garden and are considering putting mesh over the timbers
to stop the cat from coming through.

in their defence there is not a lot your neighbours can do to stop their cat
(speaking as a cat owner here ). Also a fence will not work. The cat
will just climb it. The best things to try are water attempt to drench teh
cat with jugs, water pistols, a hose etc, preferably when they can't see
you. this usually works. The other thing I've found works in pepper dust.
Hayley