Anyone have a working method for deterring cats from using my garden as
a litter tray? I have two toddlers and I'd rather they took precedence
over the neighbours cat. I've so far seen a few methods, any comments on
these:

1. ultrasonic screamers (with IR detectors to trigger them)
2. water squirters (ditto)
3. aromatics
4. "zoo poo"

While humourous replies are always welcome, this is a serious question -
cat crap is pretty toxic and smelly stuff, I don't want it in my garden,
and I imagine I'm not alone.

TIA

John