There have been many many threads on this, coldstream - most have suggested that a water pistol is the most effective method of deterring them, or buy one of those electronic cat deterrents.
or if you live near a Zoo, Lion droppings....they don't like citrus, some some orange peel where they generally"go". As you can tell I've tried most things, including white pepper and cat pepper
a pressure washer could seriously hurt an animal... pricky prunings where they go., put netting over any bare soil, as they especially like seed beds and soil prepared for planting
sadly you can't!................short of sitting up 24/7 with a water pistol at the ready, you've no chance!..............that's just cats!...................