How do you have sex without "you know what" getting everywhere?

This is gonna sound crazy but I've never gotten in the habit of watching porn. My porn is just photos of hot guys with big hard members. I think I'm a top and i've fantasized about topping. But that being said, i'm grossed out about possibly getting poop on my dick. Also does it smell bad? I've been sexually repressed my whole life by a christian conservative family so I have no idea how this stuff is supposed to work. I'm 21 btw.