PLEASE don't hit is penis.... How would you like to be slapped with something on your vagina or penis every time you were relaxed???????? Every time he drops, make him work. You can INJURE his penis by hitting him!!!!!! Especially the tip of his penis. The tip of any animal's penis or the clitoris is EXTREMELY sensitive. When you clean his sheath, teach him to "drop it" and "hide it." Eventually he will learn to put it away.
It's All A MysTori