[oneofmanynameless]

I'm wondering if there are any rules for focusing ones active defenses to protect certain locations while leaving other places open.

I.E.: I want to focus on parrying any attacks to my abdomen but leave my shoulders, upper back, and head open (e.g. hunching over and pulling arms in to cover abdomen)

In theory this would give you a bonus to defend against any attack to the chosen location, but prevent you from making any defense to the exposed location. This might seem like a stupid idea, but if the exposed locations are heavily armored and the protected area is not it would be a useful trick to know how to do. Anyone have any ideas?