There are many reasons dogs dig holes, none of which are usually met with any enthusiasm from the people in the household. A dog burying a bone or other objects, like expensive bully sticks, bones, antlers, rawhides, or other chew items, may also not be what owner's want.
Zuzu had never shown any interest in burying anything. . . until recently. On one of our off-leash walks, she caught a small rodent. While she has an excellent “drop it” in the house and the back yard, her “drop it” when it comes to extremely high value items (I won't gross you out with the details) on our off-leash walks, drop it is still a work in progress. I'll skip the other details and get to the part of the story where the small rodent is now deceased, and Zuzu can't decide what to do with it.
At some point, she decided she was tired of carrying it around and had the brilliant idea of burying it for safekeeping. She dug a small hole, set it in the hole and stepped back. Then she changed her mind, and picked it up. She moved to another spot and repeated her actions. Then once more. Finally, she decided she was not going to bury it after all.
Then the next day, she managed to sneak out into the back yard with her antler chew. The antler is in the house and not allowed outside, and while it's setting out most of the time, she only chews on it once in a while. For some reason, she decided she needed to take it into the back yard and bury it. Again, she dug a small hole but then decided against actually burying it. I'm not sure if she decides against burying it, or is she is worried that someone else will come along and dig it up when she's not there.
So, at this point, she has not actually buried anything. But she's showing some interest in doing so. In this case, digging has a purpose. How many safe spots do dogs have to keep their valuables? Burying is a way to potentially safeguard valuables from others.
If you have a dog who does bury things and you don't like them digging holes in your back yard, you have a couple of options. One is to not give them anything worth burying. Another option is to provide a particular spot in the back yard where they are allowed to bury their treasures, so that it's limited to one area and not your entire back yard.
Some dogs will also try to bury things in the house. They might use couch cushions, dirty laundry in the laundry basket, blankets, or other things they can move around to hide or bury valuable items.
While you can try to stop the behavior by taking away those options, it will help to allow them to “be a dog” by providing some acceptable options for doing what comes naturally to them.