[kikimama]

That is a shame. I know how frustrating it must be, and we do get so attached to our cats.

One of our cats used to frequently do the toilet in the hall, or other places, she also gets cystitis fairly regularly. The vet suggested using Feliway, a plug-in diffuser which is meant to calm them. I think it did work a bit, as she doesn't tend to go anywhere except the litter tray now. Though she's not totally cured, she quite often misses, and I'm not sure she was ever taught to cover up after herself. You plug it in near where they usually sleep.

Apart from that I guess the only thing you can do is start closing all the doors to rooms you wouldn't want an accident in (I know, that's probably all of them). It is a pain, but we do love our cats, it would be very hard to let one go, I know it was hard enough a couple of weeks ago when our other cat had to be put to sleep, she was 13, but had kidney problems.