You may need to place more boxes in your house. Change to another litter and
or confine him to rebox train him. Does he use his box to pee at all? Has
the vet got him on a special food? Is he on other medications? Did they
check him for bladder stones? Bladder stones will make him go randomly and
he will try to go to the nearest available spot instead of the box.

Shadow Walker

Is it possible that he is still quite uncomfortable, even though he spent
time at the vet clinic?  Can he be given some type of (veterinary)
painkiller, at least for now, which would aid in his finding the litterbox
less disagreeable?

Perhaps you could put extra boxes down, at least for now, in the spots he
has been urinating.  I would clean those spots with viniegar - - - it
generally turns cats off -  - - and then put extra boxes down, hoping to
encourage him.

I read another post to you about putting him in the bathroom or a small room
with the litterbox to retrain him, which is also a good idea.

You should speak to your vet, however, just in case there is some residual
pain which is causing him distress and the possible resultant "peeing
communication".

22 years ago, my cat Aja had major problems with crystals in his urine and
FUS.  He had repeat vet visits because of blockages, and scarring of the
urinary tract because of the repeat infections and blockages.  Surgery
helped almost not at all.  He would get desperate and telegraph his pain by
peeing indiscriminately, and sometimes even spraying (although
neutered)......one time right into the blast of air from an electric fan.
(He was not impressed when it all smacked him back *g*)

I believe that veterinary medicine, as has human medicine, has advanced
substantially in the past 22 years.  Much more should be able to be done for
your boy than was able to be done for mine.  I would discuss seriously with
your veterinarian if there were some medication that would take some of the
discomfort out of the urinary tract.  There are painkillers for humans to
tact specifically for UTI, why not animals?

I wish you and your furry friend the best of luck, and keep us posted!

Mel

He is possibly associating the litterbox with the pain he felt while
urinating in it - he may think the box is responsible for the pain, and
that if he goes somewhere else, it won't hurt.  Dr. Elsey's Cat Attract
litter contains a special mixture of herbs that attract the kitty to use
the box.