Intentional urination in bedroom

My four year old boy seems to realize that urinating in your bedroom is wrong, but does it from time to time to just be spiteful?  I have no idea what to do with this behavior.  He will come out of the bedroom during his nap if he needs to use the restroom, sometimes more than I want.  I do not keep him from going.  Today after putting him down for a nap, he jumped to his lower bunk bed and peed all over it.  I heard him in there and walked in.  I had smelled a hint of pee and made my 13 year old use his keen smelling senses to verify that the liquid i found on the bottom bunk was pee.  How do I handle this?  Any suggestions? My four year old is doing it intentionally and lying about it.  

[Kevin Kennedy, Ph.D.]

Tell him to stop it and if there is any recurrence he should be placed in time out (seated quietly in a chair) for ten minutes.