A digging stick and a beater stick (for jungle travel) will work but I'm talking about a survival situation where you need to do it now and need it done quickly. With some practice using a knife for digging is not a problem. You need to be careful but on a 7" or 9" blade even if you chip the blade you will still have plenty of blade. A far as dulling the blade it can happen but if you’re careful you should be o.k.. Also, you do pack a sharpener right?

I realize that using the knife in this manner may be considered abuse by some and yes you could argue till your blue in the face that you should use a proper tool for the job. But we are talking survival here. In my mind that means you are in a dire situation with limited tools.