Q&A: How do I stop my toddler from hitting?

Q: I have a quick question with probably no easy answer. Our son is three years old and he's exploded into a hellion almost overnight. Right now he is really having a problem with hitting. My first impulse, of course, being to reinforce the very behavior I don't want by slapping him back. Obviously, that won't help. Do you have any suggestions on what we can do to curb that? Or any websites that would offer some suggestions or resources? Thanks! —A Mom