Baby boys (unlike baby girls) can pee on many, many things while you're changing them. If you didn't know that, it's valuable information to have in your repertoire of knowledge. You can stay dry by purchasing these, which I am totally smitten with. However, if this is one of your major concerns you might want think about having a baby (pee, by far, is one of the cleaner fluids to hit you).
Who could not love something named Pee-pee Teepee?