I presume you have tried the usually recommended remedies; curry powder, moths balls, etc. all quite good if you have a garden the size of a postage stamp. I have found those electronic things to be useless.
You are actually lucky that they do it in one corner. Easier to clean out than when they do it all over the place and dig up your planted seeds and young plants. This is how we managed to prevent our cat from cr@pping in everyone else's garden when it was alive.
If it is your own cat just wrap and bin it or if there is a poobin near, use that. If you know it is a neighbour's cat and they are aware that their cat is causing you misery, send it back where it came from via airmail.