Sal - I'm with Don on this (actually, I agree with Don on everything - the man does ATG on his head!! ): I go by feel also on the back of the head. Really, I think that is the only practicable way to do it. Secondary mirrors may work, but positioning them and getting used to looking at a reflection within a reflection just sounds like more trouble than it is worth to me.

There are some things you can do to make your life a bit easier in that area though. My biggest concern when I first started was, believe it or not, making sure I did not leave little strips of hair down the back of my head. To aid with that, I have found being very systematic is the only way to go - when I re-lather to do the back of my head I make sure to lather back up on top of my head a little so I can keep track of where I have been with the razor.

Also, to aid not scalping yourself down the back of the head, you can for most areas still see the scales in the mirror, if not the blade. Watching the scales as you do the back of the head is, I have found, quite a good way to keep track of both the blade angle and the blade position.

James.