Calipso, I've read Georgesgran's post over and over, and can't see any mention of a shotgun, nor are there any references to shotguns in anyone else's posts. I think you may have misread something somewhere...?
I like cats, have been a doting cat-owner myself over the years but I do acknowledge that cat poo in the garden is not the most pleasant thing to have to deal with, particularly when your own garden becomes a target for several other cats to use as their "convenience", as mine is now. Not sure what the answer is apart from shooing them off when you see them or those spikey things on top of the borders. I'm thinking of installing those as they may also deter the wood pigeons and magpies from perching on my fences and pooping down them!
As an aside, tortoise poo smells absolutely horrible and I have to clear this up every day as well! My tortoise insists on doing her business close to the house on the patio rather than in a far-flung, inaccessible place!