The Reid wrote in
:

Does anything actually work at discouraging cats from using an area as
toilet? The product I tried had no effect (no need for shotgun type
suggestions, I don't hate cats).

Hi Mike, Now look what you've done! )
I think the best cure for the cat problem is to invite all the very
friendly people who have helped make this rather long,but definitely
amusing thread over to your garden,and then ask them the cat question
again.
The ensuing(cat fight?)discussion will keep all the cats away.

And,if anyone thinks I'm a troll and wants to kill file me,well too
late,I've already kill filed all of you.

Hello,Hello,is anybody there,it's gone very quiet in here....mmm.
LOL.

Sorry Mike,couldn't resist it.
In answer to your question,the only cures I know work are,the shotgun
type or,a physical barrier.If the area to be protected is something like
a seedbed,then a covering of fleese works well so long as its raised from
the ground a bit.Of course using fleese has a lot more benifits than
keeping cats off.
As for the rest of the garden,well,best of luck.
Hope this helps.