In addition to some earlier good suggestions, for a more permanent loop of cord, you could try...
A) Lashing the two ends of the loop together to form a circle. If done well, this is considerably more secure than a knot. I have a monkey fist keychain that is held to my keys with a lashing that's at least 5 years old. Several people at my old job also had them, and I've not heard of a failure yet.
B) Taking a needle and some fine twine (like #2 whipping twine) and sewing a few stitches through the body of the knot
C) If you like lashing, you could lash a little loop around the PB, then lash another little loop in the other end. That way you have a single cord connecting your keys to the PB, and not a loop.
Now all I have to do is to convince my wife that I need a Prybaby. Maybe I can snap off one of her paring knives...
Edited to add...
Peter, if your wife is doing your web design, let her know that there's some weird error on this page..
http://www.atwoodknives.com/prybaby.htm The title of the page in my IE has some weird symbol in the middle. Looks to me like she's trying to put the little "Registered Trademark" symbol above the main line, and that IE 6 isn't parsing it. Site looks good, and you have great pics!
