Ok,
I stand corrected, but I still think a turtle shield would fit thematically with a Kappa. After all, they wear a turtle shell on their back.
And maybe they would only lose fatigue if they suffer a blow to their head, since that is where the depression is that holds the water.
Or you could let them buy a Shisha, capital only for 250 gold
each!
http://img66.imageshack.us/my.php?image=shishivs6.jpg