I'm a huge fan of old-school tailor's chalk. The solid kind that comes in a square and you use a plastic holder for it, or in a sort of triangle. I have it in red, white & blue and between those colors I've been able to mark pretty much everything. Never had trouble with it not washing out afterwards.
Like this stuff:
http://www.amazon.com/Dritz-642-66-2...ilor%27s+chalk
Or this:
http://www.amazon.com/Clover-Triangl...ilor%27s+chalk
It sticks to the fabric much better than the Chaco liners do. I like those too, but the old-school chalk wins as far as durability - the Chaco liner chalk just lies on the fabric and can brush off too easily for your use, I think. The tailor's chalk sticks much better.