Thanks for the tip- I'll definitely keep it in mind, though it might not work with all folding knives. I'd have to experiment to see if there's room for the blade to close completely (so the point is covered, at least). Oil does help in cutting... but maybe not with peanut butter.
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For the moment, for running and sailing, I got a relatively inexpensive OceanMaster titanium folding knife:

http://www.oceanmaster.com/KnivesFeatures.htm ("Server")

that seems impervious to anything, and is amazingly lightweight... but I'm not sure the edge would hold up for constant use.. it's meant for emergencies. For sailing I also own a Myerchin LightKnife:

http://www.myerchin.com/L300.html

.. but, while it's impressivley sturdy and functional, I've found it pretty heavy, bulky and magnetic (a concern if you're at the helm).

I think Chris said he's partial to MyerChin knives.