Get a few of those large upside down triangle dog leash holders with the corkscrew bottoms. Put those in the ground all the way and use packing straps with the ratchets on them to tighten the staps to the canoe.

If the ground gets wet enough not to hold those corkscrews, then I think you're canoe would be gone no matter what you did. If you have lots of sugar sand and can't get down far enough, I don't know what to tell you! Perhaps some sail rigging rope and just "fly" your canoe. Might want to put it on the highest part of the house so it can wind vane! <img src="/images/graemlins/smile.gif" alt="" />