OK folks - the law.
(This post only applies tio the UK)

If a cat is continually fouling in your garden and you can smell or, God
forbid, come in contact with it, it becomes a statutory nuisance under
Environmental Protection Act of 1990 and the local authority can take
action. Thus, the cat has become a health hazard under the said act and,
also, under the Public Health Act 1936.

The more complaints that are made to the local authorities (and your local
councillors) the sooner cat owners can be made accountable for their cats
filth. Remember to quote the Environmental protection Act 1990 and the
Public Health act 1936.

MC
The war has begun.