Actually, the cord was being walked on, not being entirely shielded by the tread; I think what made it work was that rather than just wrapping the cord around in circles, we criss-crossed it from both directions, hooked it on the lace hooks at a few points, back around the heel, etc., which kept it from just sliding off the toe end.

Come to think of it, the fact that it was a boot rather than a low-cut shoe probably made all that wrapping possible.