Shields: parrying melee while dodging arrows


I don't know if this has been asked before but here goes; can a shield provide both a parrying bonus while in melee and, at the same time, provide a dodge bonus from arrows?

I ask this because you are either supposed to be parriying or dodging not both at the same time. Hmm, even without a shield, can you parry a sword and dodge an arrow in the same round?

If possible, is there a penalty involved? Should I assume that the victim can only pay attention to either the melee attack or the range attack?

It should make an interesting situation; try to parry the greatsword or dodge the envenomed dart.

I think I'll rule that he can only pay attention to one or the other and use these formulas for DV:

-Parry melee ignore range; DV(parry)= 10+parry bonus+str+other, DV(range)=10 +dex

Essentially he will be denied the bonus (parry or dodge) of the attack he chooses to ignore.

Your thoughts? Suggestions?
By the book you can freely choose to parry melee attacks while dodging ranged attacks. There's no restriction or penalty. In fact, the shield you're carrying can be used for both as well!

Feel free to change this if you desire but I prefer to keep my rules simple and as close to the printed materials as possible.
Maybe you are confusing Melee vs. Finesse attacks? You have to choose which kind of attack you are using at the beginning of a round. But choosing to defend via dodge or parry is referred to as "a Free Action" which suggests you can decide each time you are attacked (before the dice are rolled, of course).