Chosen answer:Earlier in the film, it's mentioned that he had some money buried in a special spot in his yard, but that it had been dug up. When he saw the shovel at the end (which indicates that something was buried that he should did up), he realised that the new money stash had been buried in the same spot as his old stash. They basically gave him the clue, and he put two-and-two together on his own.
Chosen answer: Earlier in the film, it's mentioned that he had some money buried in a special spot in his yard, but that it had been dug up. When he saw the shovel at the end (which indicates that something was buried that he should did up), he realised that the new money stash had been buried in the same spot as his old stash. They basically gave him the clue, and he put two-and-two together on his own.
TedStixon