I've been owned by cats all my life and have never had this problem before
now.

The problem started when we rescued Hunter and he was kept in the upper
three bedrooms, bathroom and hall (we installed a door at the end of the
hall to keep him in and the other cats out).  He was an intact tom for the
first week and a half we had him until his "snip" could be scheduled.  I
wasn't surprised when he started marking his territory (even though our
current clowder, 2 girls and 2 boys, were already desexed) - that was pretty
standard behavior for a tom being placed in new digs.  We cleaned up with
"Nature's Miracle" whenever we found a new marking (we bought a black light
to look for stains not noticeable to the naked eye).

As most of you know, Hunter died suddenly, after we'd had him for only 5
weeks, from a blood clot "thrown" to his lungs - we had no idea beforehand
that he'd had myocardiopathy, 3 vet visits by two different vets didn't
detect it.

Even though we thought we'd cleaned thoroughly, apparently we didn't.
Somebody started peeing first in the guest bedroom where Hunter had spent
most of his time, then in DH's office which was Hunter's second favored
spot.  We cleaned again, thoroughly (I think I'm supporting the stock
holders of "Nature's Miracle" by now), but it continued.  So then we cleaned
yet again and closed off those two rooms (our house is big enough that the
clowder still has lots of room to roam despite that).

For a while that seemed to have solved the problem, but yesterday when we
got home somebody had peed all over the stair landing.  I know for a fact
nobody, not even Hunter, had sprayed there previously, so this couldn't be
somebody trying to overlay a scent mark.  DH thinks somebody may have been
playing, gotten too excited, or too involved, to make it the rest of the way
downstairs and into the garage to the litter boxes.

I'm now pretty much at my wit's end and don't know what else to do.  There
is absolutely *ZERO* tension in the clowder - everyone is great friends with
each other and they groom and play and sleep together, so I don't think a
Feliway diffuser will help (it didn't keep Hunter from spraying to begin
with when we were using it then).  Cleaning with "Nature's Miracle" doesn't
seem to help - they keep finding new places to pee.

DH caught both Archer (male) and Sammy (female) in the act of peeing in his
office, and I found Ozzy with a wet butt once, so it is different cats
spraying in different places.  This makes me think it's a behavioral issue
rather than a health issue like a UTI.  Archer, Demi and Sammy have all been
to the vet within the last couple of months and checked out just fine.
Jessie and Ozzy haven't, but haven't had any changes in eating or playing.

I really don't know what else to do at this point, so any other advice
anyone may have would be greatly appreciated.

Hugs,

CatNipped