Lots of different things, you can buy lion poo (it doesn't really smell) and put that around the edges of the garden also if you have a spare male to hand then they can "water" the edges of the garden, also there are various plants you can use as well, i have used curry plant in the past and that worked fine for me. i'm sure others will have more suggestions.

Thank you Catty4667.

If its your cat, I'm assuming your plot is at home in your garden rather than on an allotment. If that's the case, dig over somewhere else in the garden - the borders, flowerbeds, whatever. The only reason your cat (and others) is going there is because the soil is nice and loose and easy for them to move around and cover up their doings, so if you make all the soil looser, they'll have other, different places to use.

You can buy little cat deterrents, they have a sensor that detects movement ans sprays a jet of water at the cat. A friend of mine has a few dotted around his garden and it's funny to see the cats scoot when they're sprayed. The good thing is that after getting sprayed a couple of times they learn to keep away from the nasty area that wets them :o)

Your cat, your garden. The cat has to do its business somewhere and your own garden is more appropriate than the neighbours. If you don't want it doing its stuff in the beds then provide a litter tray for it.

Plus if you remove the earth that said cat has already used to the tray thereby putting its scent down it hopefully will encourage the cat to realise thats where you need it to go, luckily mine only use one area so I allow them to go there, it makes life a lot easier...

Sticks.
I have used my Buddleja prunings layed on or stuck into the ground to stop our cat sleeping on plants. If they are close enough the cat can't stretch to dig or squat. When the plants grow he/she won't use it anyway, and you can remove the twigs.
It's cat friendly, green and easy.

Cats and gardeners don't mix well together. Solution - get rid of the cat!

Tongue placed firmly in cheek and tin helmet tightly strapped on!

I have an enormous vegetable garden and one cat who turned up as a stray, not a house cat. I have tried making well dug areas, even in the veg. garden for her but alas, she digs where she pleases. This is only a problem for me when I have freshly seeded as the seeds are dug out. Once they are up she doesn't touch the row. Until then, I over the rows with chicken wire, short metal edge fencing flat on its side and even tomato cages stuck in. This works. I have always had stray cats around for the past forty years and have never, been able to keep them out of the garden. I have separate flower beds, well dug but no, the veg. garden it is.
A friend in town has neighbours cats, none of his own, come into his small flower garden. He has tried everything you can think of, many of them not very kind, they still return. Possibly not the same offender. I think one has to learn to live with it.
Clementine

Thanks all for ideas, i have used chicken wire as a cage on veg patch & although it looks unsightly its doing the job. i did just lay it down on top at 1st, but the cat still used it as a toilet (our cat is a bit of a weird cat) i have barked flower borders & it still uses them. I will have a look for some sort of repellent to put down too. I have a motion detect scarer that emits high pitch sounds to scare foxes,(of which i have problems with too) cats & birds, its as much use as a chocolate Tea Pot.

Thanks Again guys.