There is a point, however, where there are rapidly accelerating negative returns on avoidance (I've never calculated where the best place to stop stacking is).
The mantra I recall was: Parry rating gets to be better avoidance per point than dodge when you have ~700 def, ~700 dodge rating, and ~200 parry rating. I do not think this is a point any of us can actually reach, though -- therefore it's effectively never going to happen.