How to make the rotation constraint not being affected by a parent of a source ?

I have a problem with rotation constraints, when I set up a source, the constrained object rotate with the source, until then everything is ok. But when a parent of the source rotate, the constrained object also rotate. this is annoying, for example if I want to control/sync the toes of an avatar with my fingers, when I ll be moving my arm (parent of fingers) the toe will also move