Its a natural instinct I am told. Ours does it with fox poo if he finds any. Mind you the last great dane we had was at a time when we ere raising cattle in a small way, and there was nothig she liked more than finding a liquid cow pat and slurping it up. She was also fond of putting her front paws on your shoulder and licking your face. Put the two things together ...............

Present dog is 20 months old springer poodle cross and is absolutely manic. Doesnt matter how long the walk is, he starts running and runs all the time and finishes running. In between diving into the river and digging in the river bank.
Are you anticipating the demise of the older dog in getting a pup?