I don't know what to do about my cat...

 Hmmm, a kennel for the cat!  I like that idea!

LOL - we use an ex-pen with a top for ours, but I'm sure Pi would prefer a cool basement like yours. ;)

Not a bad idea, really. That would re-train him to use the box too - since he wouldn't really have a choice. Our cats are 'kenneled' at the shelter - and do just fine (some are loose too)

Maybe I could just put him out on the screened summer porch during the day.  He likes to be out there.  My females don't even care they are also blocked in the basement, they prefer it there and only come out at night, but Beckham keeps howling and trying to bash down the cat door to get out.  I think porch/basement is a fair compromise? 

That sounds like a great idea....you could alternate between the porch and the basement too!  Essentially, you just need to keep him away from that specific area.

Boy, I just saw this post and understand your frustration. We have 3 cats; all seniors (13-18) - one with kidney disease, one with IBS and one who has just started marking all over the lower level of the house. The crazy thing is he'll do it right in front of me. We have been to the vet, ruled out infection, tried the feliway diffuser. I am at my wit's end. I can deal with kidney disease cat and the daily IBS vomiter, but cat spray is a whole different matter. I am SO frustrated and find that my tolerance is wearing thin. I feel terrible - I used to be such a cat person, but honestly its doubtful I'll ever have another cat again after this. Our vet has prescribed an anti anxiety medication for the spraying monster - apparently he has had some success with it. He gets his first dose tonight. So I'll let you know if we have any luck. The really tough thing is that I love the super-sprayer dearly, but can't handle having the house smell like pee.

Liesje - The med my vet prescribed for the super sprayer is clomipramine. I just did an online search and one of the sources I found says that it is 90% effective in treating inappropriate marking behaviour. So far he has had one dose and I will say that it seems to have taken the "edge off" for him. He is normally the trouble maker, even at 13 picks fights with the other two, knocks stuff off the counters just to watch it fall, paces, throws himself at closed doors etc. The ultimate Evil Mr. K. Will keep you posted as to whether it works. Lets hope so as in the last 4 weeks he has sprayed my knitting bag, the dog bed, a painting, the bathroom and the bath tub.