how do I deter a very determined cat?

If you have all the time in the world then a water pistol is definately the way forward.
Or a dog.
Good luck.

You can get a spray from pet shops called Shaw's Repel-All.Here's a description of the product....Shaws Repel All indoor and outdoor dog and cat repellent. Specially formulated to keep pets away from your furniture, carpets or other places, indoors and out. This non-staining formulation is harmless to most furnishings and harmless to pets. The smell is naturally very unpleasant to animals and they quickly learn to avoid it.

Hope this is of some help.

Try prickly cuttings like Holly in the pots. It stopped the squirrels from digging up my bulbs, it might deter the cats???

I have a cat & heron scarer for my pond I think you could use it for your flower beds, the cat's will not like getting wet and they may stop visiting your beds. I have put a picture on my photo's. Good luck. Jackie x

Is it a male cat who is marking his territory by backing up to your planter and lifting his tail? or is it a potty thing?
Cats are territorial...especially males...and this may be why he is especially determined to use your facility...so to speak... you have to assert territorial dominance...my father had an especially interesting and effective method...he grabbed the broom and brandished it at the cat while making a loud hissing sound...cats beat a hasty retreat!! other than that the dog as deterrent was a good idea...know anyone with a dog they could lend you for a day or two? also, have you tried garlic?

Cats like nice soft dry soil that is easy to dig in. Pea-sticks stuck in the ground deters them, but getting a good cover of plants all over the soil will mean puss can't get access to the soil and will go elsewhere. In my veggy patch I use 'Scoot' which is a powder you mix with water and water it onto the soil with a watering can. Works for me,.

My sympathy, I have the same problem but have resorted to chasing the so&so and showing him my foot calling him unholy names. I trained my cats to use a litter tray so my neighbours were not offended. I did ask my local zoo for some lion dung to put on the garden perimeter but retrieving the matter is dangerous apparently!