Bluebelle.... I've had cats for 38 years. All have had litter trays, but one of mine used to use our own lawn as a toilet! The remaining cat I've got now never ever uses a litter tray. He's got one here (all clean and fresh) and he stays in all night but doesn't use it. The one and only time he used it was when we were on holiday and the cat-sitter didn't call here as he should have done.
Cat owners have no control over where their cats go. I don't think there's yet an effective deterrent
To go through chemo therapy or choose not to?