I love cats.......but not in my garden......

This post probably arises from my total frustration at constantly finding cat faeces buried in my garden and polytunnel when gardening.
I love cats but how many cat owners behave responsibly in this respect?    Very few, I suspect.
A developer has built 5 modern houses backing onto our productive vegetable garden. As a result there are 12 cats owned by those individuals that are allowed to roam free and all appear to use our 30ft polytunnel as a toilet.
Growing salad vegetables has become impossible because of the health risk and it is not very pleasant having to deal with it.  Its time society took this on board instead of constantly carping about dogs.  At least their owners are under considerable pressure these days to clear up after their pets.
Have a cat by all means but keep them in overnight and train them to use a litter tray for their 'requirements'.....