A cat-a-pult and a dog sound like great ideas.

She's never go for the cat poop as fertiliser Jay. Tel the garden is fenced off but they just get over the tall fences. I have mentioned the idea of cat nip to her though, so that's a possibility.
Thelma these cats seem to like the soil what ever it is and like I mentioned they only seem to go on the South side of the garden. I did mulch it but this just seemed to attract more poo. she doesn't do her garden much as she has a bad back so it's not really tilled and I've not tilled it for ages. I have suggested that she try to fill her garden with as many plants as possible. They poop on the lawn too so not sure how will stop them doing that. I think I'll keep encouraging her to buy as many plants as possible to stop the little critters.