Pickles was adopted as a juvenile, and started spraying the next spring. We tried Feliway, enzymes, and finally kitty-prozac, but nothing stopped him. In retrospect, I think it was our little critters upsetting him. We tried for four months to get him to stop. He even sprayed gifts from Gary (catmandu) as soon as I opened them.

*edit* Just wanted to add that once Pickles settled in at the animal shelter, he stopped spraying. This is what leads me to believe our mice/birds were causing his upset.