I have an elderly relative, who is fairly unwell and infirm.

Lately she has been having a problem with an unknown cat, which is pooing at least every other day right on top of her small back lawn, where she goes to hang her laundry on the line. It's also a bit odd - all the cats I know seemed to like covering the evidence in earth, not going on top of grass and leaving the evidence out in the open.

As well as being a tad unsanitary, this is causing her a bit of distress and annoyance.

I have tried the vaporub approach which some colleagues have suggested (rocks with Vicks Vaporub smeared on them, as apparently cats hate the smell) which hasn't worked.

Interested in anyone who has any tried ways of repelling cats that they know to work.

NB: She likes cast and so do I. So not interested in anything out of the Gareth Morgan playbook that could harm or kill whichever cat it is. Also, trapping could be a non-starter, as there are a lot of cats around - and presumably only one culprit.