This I have discovered, is not a unique problem. Even one of our own SE bloggers posted about the issue a few years back and hilariously they were advised to use Lion Poo. http://plumssel.blogspot.com/2007/09/roys-stores.html
Now I'm not sure about that as it seems to be replacing small moggy poo with large ferocious beastie poo. So we are trying other methods.
When we moved back to our house last year we noticed cats were using planters filled with pebbles as their own personal litter trays. I chucked those out and we got a sonic device from B&Q. That works well as long as the batteries are working. So yay a batlle won and we have a clean patio.
The war has moved to a new frontier...the front garden. As I want to replant this, we have been simple digging the soil (that's what it's called according to Gardener's World). But the soil is in poor shape and we have to replenish it with manure. That doesn't arrive until Friday so until then, I have to keep the cats off.
Hubby got an even more fang dangle sonic repellent and ...it's not working. So I bought curry plants from Thompsons.
This morning there was more poo. So I have placed the curry plants strategically and have also doused the whole area in chilli powder. Had to wear some glasses as the wind blew the powder straight into my eyes and stung like hell. I feel a bit guilty that the cats are going to be hurt but it's only temporary and all's fair in love and war. I do wonder if curry restaurants have a beastie problem as they must always smell of curry. I also wonder if it is worth just dumping left overs from curry dinners in the garden...bit nasty for us to watch it decompose though.
If this doesn't work we still have the following options: