In town, you may attempt to hit each rock with a tool to shake it out for money. You may continue your shake down until this rock exhausts itself. This manner of money-making may be done once per day.
When you hit the rock, money will come out. However, you will bounce back. You will have to run back to hit it again. To prevent this, dig holes around you in a pattern so that you won't bounce away. You can make 20,000+ bells a day this way, but you have to be fast to get this much.

Submitted by Rex Monkey-654
Improvement by Shadowlord96