+1 with what NurseMike just said.

Soldiers sometimes wear a knife upside to give them quick access in combat. But unless you feel directly threatened and you are using your knife for self-defense - then this is not your best solution for survival purposes. Better to just attach it to your pack ... maybe the sides, or the back, of the pack. Try zip ties or small leather straps.

Large knives, machete's and parangs can be useful in some environments (esp. jungle) - but they tend to be heavy. Take a look at the knife that Bear Grylls uses - it's not that big (Bear uses a Bayley knife, can be seen at Bayleyknife.com, but they cost a small fortune!).

otherPete