Three things to try, two depending on what's in your kitchen cupboard - they've all worked for me in the past: 1. Coffee grounds and slices of orange or lemon peel - mix them together then spread around the flower bed. Cats don't like citrus and they hate the feel of coffe grounds on their paws. 2. Vinegar spray - mix equal parts of white vinegar and water in a spray bottle, then add a squirt of washing up liquid and shake it up - spray around the flower bed. 3. Plant lavender around the flower bed as well - cats hate the smell of it.