Start by making the planter less attractive than the ground around it. Cats usually choose loose, dry, bare soil because it is easy to dig. Remove feces promptly with gloves, then clean the area with mild soap and water; avoid ammonia-based cleaners, which can smell like urine and invite repeat use. Keep the soil surface covered as much as possible: a layer of large pebbles, decorative rocks, or a tight grid of twigs can stop digging. For a softer look, use prickly mulch such as pine cones, holly leaves, or coarse bark, but check what suits your plants and local climate.
Physical barriers work best in urban settings. Lay chicken wire just below the soil surface and secure it at the edges, or fit a removable wire grid over the planter. Netting or a light row cover can protect young plants, and a low decorative fence may redirect cats. Keep the soil moist and not freshly turned; cats prefer dry, loose dirt. Watering with a drip line also makes the surface less pleasant without harming plants.
Scent and motion deterrents can help as backup, but use only cat-safe options. Citrus peel, coffee grounds, and strongly scented herbs such as lavender or rosemary may discourage some cats, though results vary. Never use mothballs, essential oils, bleach, or poison—they are toxic and cruel. A motion-activated sprinkler or ultrasonic device can be effective, but urban cats may become used to it. Move deterrents around every few days so cats do not get comfortable.
Give cats a better option. If the cat is yours, keep a clean indoor litter box and make sure it is large enough. For neighborhood cats, talk with neighbors about shared solutions and support humane TNR (trap-neuter-return) where legal. Finally, plant densely, top with ground cover, and leave no bare digging patch. Consistency matters: combine a physical cover with safe scent deterrents and regular cleanup, and most cats will choose an easier bathroom spot.