Thanks for your kind and helpful replies. I think we should try the citrus. We almost always have citrus fruit in the house so getting the rinds won't be a problem. We don't blame the cats for their trespassing ways. They are doing what comes naturally. If we knew who owns them we could at least ask them to be responsible. It does get old having to clean up after someone elses pets though.

This is the nice little kitty my husband was feeding...LOL
http://curiouslylocal.com/2010/02/589/

I think that if you sprinkled pepper on your flower beds, that would work, though you would have to renew it every so often. That's what I used to do round my shrubs.

I now have one cat, Meg and she is over 16 stayes inside mostly. My problem is strays and feral cats, possums etc that urinate on my deck and rockery.
I desperation I went to the local pet shop and they suggested a product called 'Urine off' deters the animals and gets rid of the stink. cost me about $30 AU (larger spray bottle) but worth every cent has lasted for two years and just about all my friends have used it.
possums love anything citrus. The possums usually spray on my army gear when out bush with our army cadets. Now I take some spray with me cause isn't anything worse than possum smell in the tassie Summer.

Thanks for the tip about the possums. We have those and armadillos, as well. I'll have my DH look for some Urine Off. I hit a possum once with my car. I stopped on a dime when it ran out in front of me. I waited for it to get off of the road before I started going, again. Wouldn't you know it the darn thing ran right back out into the road and I couldn't stop that time. The smell was awful, as bad as a skunk. I felt bad for it and worse for me. lol The $30 would be worth it if it works. :)

There are Motion sensors on Tv that r suppose to work and not expense. Look at as seen on tv .com.

I had to resort to nailing chicken wire over my flower garden(it was covered by the walkway overhang so always nice & soft & dry) as the neighbour's cats were always digging up my bulbs. It wasn't fun trying to plant seedlings through the wire mesh, but it kept the peace. Our dog would go crazy when he'd see the cats, but alot of the time, the cats came at night.
I have heard that the crystals used for toilets/urinals or mothballs will also deter them, but they might be poisonous.

I have heard very good things about this item

http://www.amazon.com/Contech-Electr.../dp/B000071NUS

i have three cats. mamma cat goes out on a leash. our cat we lost at 17 yrs went out on a leash too.
put decorative rocks around your plants in your garden adn they won't use it as their litter box anymore. they like dirt!

My cats come around at night - not sure a motion detector would work :?