abrogard

I mean when building a wall. Because I get up on the wall and start going backwards, laying blocks as I go and I wander off the wall. Holding Shift was supposed to help but it doesn't. And of course I'd like to go quickly. So I'd like to hold Ctrl while I go backwards, laying blocks. And I find it difficult to rise in the air and stay where I want to be to do all th is 'air building'. I'd appreciate any help anyone can give on the best way to do this kind of construction. :)