MTB, You run the risk of discovery accidental or otherwise. How about doing the same thing but cover it with soil, then leaves and debris. Making a low gradual hump. Place the end of a log on the end so it could be removed to expose the end-cap of the cache. A thin layer of dirt over the cap could conceal the cache if the log is moved. During the winter months use an axe or sledge to unstick the log. Finding anything under snow is a challenge, you will need a foolproof method. I like triangulation for marking.