How old was your cat when he was neutered? If your cat was fixed after he reached sexual maturity, spraying may have already become a fixed behavior and your cat may continue to spray out of habit. To help stop it, first start by completely removing any odor from previous spraying. You can then buy special spray from your local pet store that you can then put on these areas. A few products that I have heard work are Feliway and X-O. Sometimes spraying is caused by stress. To lower your kitties stress level you should try maintaining a schedule. If nothing seems to work, contact your vet and she might be able to suggest an animal behaviorist that specializes in cat problems or have a few suggestions of her own. Good luck!