A   first take him to a vet to rule out an medical problems this is not an
option animals even though they do it occasionaly         it can be a first
sign of possible problems.  Rule of thumb is always rule out medical before
behavioral can be                 taken car off

B  make sure you clean the spot with proper chemicals to remove the smell

C  make sure you keep the litter box clean

D  make sure there is no stress in the house animals pick up and react to it

Rub his nose in it - he won't do it again.

Bob

I've found that sprinkling a generous amount of white pepper in the area
makes my kitties avoid the area..plus it's a cute show when the sneezing
begins.. :)

Offhand, I'd say it's time to see for a vet trip.  This could be caused by
any number of things, some serious.

Bill,
Los Angeles