I also use a Gerber fillet knife.  Mine is only 11" long, though, with a 6" blade.  It has a rubber-coated handle (or some synthetic version of rubber) so it's easy to keep a firm grasp on.  I like how well it holds a sharp edge for a long time with just a bit of touchup needed during the trip.

I did look at the 11' model, but elected not to get it because it would be such a pain to portage.  Would have made a nice bear-sticker in a pinch, I suppose.