Any advice on the best (or least bad) position for doing it on a roof?
I'm pointing at least some of the parapet walls on the main roof ('cos it turns out the roofers who did them 12 years ago were lying bastards). It's a typical small Victorian terrace and I have a roof ladder and fixed belay rope. But I end up either flat on my face because I slip on the artificial slates or contorted because the chimney stack keeps the ladder too far from the wall.
Or is there a further volume of the Kama Sutra that deals with this stuff?