I have a plant called Rue that is really stinky and cats hate it. When I plant, I harvest the tips of the Rue and sprinkle it around the freshly dug soil. In other areas (if I run out of Rue) I simply put stakes in the bed or cover it with chicken wire. Cats don't seem to bother the soil if the plants are established. They seem to prefer the freshly turned soil. When you buy starts from the nursery, they often put them in a black plastic tray that is sort of 'netted' on the bottom. Turn it upside down to protect small beds of seeds.