Let's face it. Some cats are just born skittish. Others are wary because they were born feral or lived in a threatening situation in the past. Anita G. writes:
Anita, the problem probably isn't the litter or litter boxes but rather Sherman's insecurity in the household. His fear is what's driving this behavior. The bed is the scent-center of the house because it's where the greatest concentration of human scent lies. By urinating there, Sherman is making himself feel better about his territory and his place in the social hierarchy. The big question is how do you help him to feel more secure? Once you've done that, this behavior should stop.
Security is a tricky problem that usually requires a lot of observation to unravel. First, you need to make sure there's no real competition for resources among the cats. Sherman should have his own food and water bowls that aren't in the line of sight of the bowls that the other cats use. It sounds like there are plenty of litter boxes, so that shouldn't be an issue.
Another resource is prime window space and sleeping places - especially vertical space. Since the bed is the center of this issue for Sherman, is he facing stiff competition for sleeping space on the bed? It may help to add taller cat trees so Sherman can get up high. More enclosed hiding places can help too. Anywhere that he can go where neither you nor the other cats will physically get to him. A small box on an accessible closet shelf or under the bed can be a perfect hideaway. Cat trees are the best because they immediately add vertical space. If they're placed near shelves, they can also provide access to high areas that help many cats feel more secure.
You'll also need to set aside special time to interact with Sherman without the other cats around. Just thirty minutes spent paying with him alone each day can work wonders. Since the bed is such a focus, that would be a good place to play. Just close the bedroom door so the other cats will give you time alone with Sherman. He'll feel better with your undivided attention and he can also spread his scent on the bed without urinating there.
Speaking of scent, you'll want to pay special attention to laundering the bed clothes where Sherman has urinated. If he continues to smell it, the scent will reinforce his behavior. Use a good enzymatic cleaner to permanently get rid of the odor even to Sherman's sensitive nose.
Observe him diligently, Anita. Notice what scares him. The other cats may be subtlely pushing him away when they sense his fear. Intervene if you can. Pet him under his chin and raise his head. You'd be surprised at how much hands on top of an insecure cat's head feel as though they're pushing him down. Help him to build up his courage and social position in the house and the problem should correct itself, but it will take time. Above all, never punish him for improper urination. All that will do is to teach him to feel insecure around you.
We wish you both the best of luck!