well as a cat lover, but also a wild cat hater i bought a cat detecter, you put it in your garden and it sets off a loud alarm that only cats can hear, check out ebay! :)
-Some flowers, as lilies. Toxins from lilies can poison your cat, as well as any other toxins - from paint, sprays, etc.
Narrow and elongated items as vases are dangerous, because cats can stock...
Simple scare them away use water to spray at them and kinda throw something in their direction but don't actually hit them that should usually keep them away