My next-door neighbour's four-year-old boy stands and wees in a corner of their patio - he was doing it all last summer and now that the weather's improved it's clear that he hasn't forgotten about it. I think it's a dreadful and unnecessary habit, especially given that they have a downstairs loo (although we don't, and DS just asks for his potty whenever he needs it). Almost as bad as weeing on the kitchen floor.