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I would be curious to know where your dog defecated and didn't you travel
through that when you mowed? I would be shocked if you could really see cat
poop in your lawn. It's very small. And assuming these cats are just
wandering through, everybody's yard is equally fair game, so by the laws of
probability, how much could there possibly be?
Best regards,
---Cindy S.

Whilst I hold cindys view, because it is very unusual for a cat to
defecate anywhere that they can't cover it over, I can also appreciate
how you feel too because my mother hated cats for nearly the same
problem.

Her problem was that they did it in her flower beds, which I am sure
must have been awful"for her"...She loved her flowers and tended them
with care, so she got annoyed when she found her hands in cat poop!!
I am sure that we can all appreciate that one even if we don't hold
with it?

If you can actually catch the offender, I would say that a hose pipe
or a water demister would do the trick for you.Cats don't like water
too much...Or a jar with marbles in it-shake it when you see them
doing it & they will skitter away..

The only other thing that comes to mind right now is citrus peelings-
they aren't very fond of it, it is natural & far easier to pick up
than poop is before mowing.
The only thing that I can suggest for your paint work is an enzym
remover. It is a bit costly, but it DOES work, so once you remove the
original marking, no other cat would marlk it afterwards, because all
they are doing is establishing an older scent remaning there... & it
could a dog! you need to keep a vigil to be certain

What ever you do, please don't try harming them though...
the suggestions I am giving you worked for my mother, so I am sure
that they will work for you too.
Good Luck
So)

There's a product called "Cat Stop," which is an electronic devlce
that makes a sound that cats don't like. I use it on my husband's
model-train layout in the basement, to prevent the cats from chewing
on the scenery, and it works well. Depending on how large of an area
you are trying to protect, you might need more than one, but they do
work.

http://www.safepetproducts.com/pilot.asp?pg=catstop_main