Cats & Coffee Grounds

morg_monster

One idea I have read but don't know if it would work is to plant some catnip, apparently it makes the cats like your garden and they won't poo in it anymore... not sure if that would actually work but isn't a big deal to try out.
As others have said you have to try a few things, espeically with the "smelly" stuff, to see what the particular cat hates. EG ours hate mint smells, but my cousins cat will try and put her head in your mouth after you've cleaned your teeth, she loves it that much... WRT to your specific question - ours show no aversion to coffee.

I agree with the others about the gripper rods, no need to hide them and you can get strips called prikka strips (I think) which do the same job but without actually injuring the cat. Cat paw + gripper rod + soil will almost certainly result in a ripped, infected pawpad which can be tricky to put right. If I knew my neighbour had resorted to that I would be chasing them for the vet bills. I know that strange cats pooing in your garden is awful but please don't actually harm the cats, there are lots of other things you can try. Scaring them is fine :-D

foxgloves

There's a plant you can get called 'Scaredy cat' which cats are supposed not to like. I haven't tried it myself.