Cats love gardens, it’s true, but many think the garden was planted for their pleasure. Besides using them as giant litter boxes, they also tend to dig up the plants as well. There are many natural cat repellents in garden centers that work. Also the herb, rue turns cats off for some reason. Many plant rue on the outer edges of the garden to deter curious felines.
Cats are very persnickety about: the feel of what they step on. They simply detest walking on stubbly, bristly material. During the mulching process add something on which the sophisticated paws of cats will refuse to tread, such as sharp-edged, but quite attractive pine cones.
Another mulch that works as a natural cat repellent is stone mulch. .It may not be the most beautiful mulch for your particular bed, but cats prefer to eliminate in loose dirt. Cats as a rule won't bother with an area mulched in stone. They prefer to dig where the digging’s good.
An alternative is to plant s separate garden bed of assorted catnip, catmint and cat grass. True, not all cats go ape over catnip plants, but those who do may come to view their "catnip patch" as their own private sanctuary and make it their new favorite hangout, thereby allowing you to keep your garden as your own sanctuary.
Why not make an outdoor cat litter box close to the cat plant garden. Yes, you will have to clean it out, but it will be easy to locate and not in the garden...
Special ultrasound devices such as Cat Stop operate on a high frequency. It's out of earshot to humans but insufferable for cats. Installation is simple. You merely place the device so that it faces toward the garden. A motion sensor detects the sweet intruder's presence, and Cat Stop then gives off its hideous, high-frequency sound.