the line that Whit makes reference to I also use and recommend. Just buy some extra line when you order your "box" as the fine line wears out relatively fast. Having a line that self-retracts is a definite bonus if you are snapping a lot of lines. I use black most often and red if I make a mistake with the black. I usually plane off the chalk lines and whatever layout lines after the joinery is done.... if it is not possible to plane the timber after joinery, as in old barn beams, I would use the technique Raphael describes, pinning a line to the timber and using the line itself as a layout tool.