You really can't stop wet dreams, since they happen while you're asleep. Sometimes guys wake up after a wet dream, other times they don't. If you're worried, try sleeping with a towel nearby. If you're sleeping at a friend's house, have a change of underwear with you.
Scientists believe wet dreams are caused by a rise in levels of the hormone testosterone that happens in a guy's body during puberty. Most guys have fewer wet dreams as they get older.
Chances are, some of your friends have had wet dreams too. They're pretty common. Wet dreams aren't a sign of a health problem, and they don't cause any harm. But they can be confusing and embarrassing at first. So it can help to ask your doctor about wet dreams or any other questions you have about your body.