I bought a second thumb guard. I keep my Case small congress in it and keep that in my pocket. I bought a bunch of 1x1x6' pieces of basswood from ebay. I keep a couple of pieces in my desk, some more in my backpack, and a couple in my car. I figure that way I always have access to some wood if I'm stuck somewhere.
So far I've done a chain, and a ball in a cage with a couple of chain links on the end. Usually worked on them at lunch if the weather's not good for a walk or if I'm outside by myself grilling.
My biggest concern is to make sure I don't close the knife on myself. I did it once as a kid and still have the scar.

It's not a major concern, just something I try to stay aware of.
mikeg