As the dog evolved in the ancient world, life was hard on dogs. Dogs had to compete with other dogs and larger predators for their meals. If other predators found the dogs food, the dog could lose their food, especially if the rival was larger than the dog. The dog had to develop a means to keep the food that it had caught and to have food around during scarce times.
For these reasons, dogs learned to bury their food, including bones. Predators naturally have a heightened sense of smell. This meant that early dogs had to hide their food from the noses of other predators, including other dogs. As a result, dogs buried their food after having a fast meal themselves. Later on, the dog could dig their food up and eat again.
Dogs also bury their food when they have a surplus of food. This insures that there is some food when the dog needs it during leaner times. Burying food to hide it from other predators and to keep for when there is a food shortage still occurs among dogs in the wild.
The food that is buried will stay at a cooler temperature than that which sits in the sun. The buried food is also less of a target for flies and insects, which would eat it. Burying food is practical for the dog.
Since your dogs instinct to bury things is present and even very strong in some dogs, your pet may collect and bury more than just bones and food Dogs are also known to bury toys and their masters items, whether this is in anticipation of hard times when all their toys are gone or the toy is so great that it must be hidden from other dogs is unknown.
Your dog will want to bury its bone or food in a secluded place, preferably near its den or your home. You can give and train your dog to use its own special place where it can bury food and bones, much like a child is given a sandbox in which to dig.
Even though a buried bone in the garden can make your unhappy, there is little that you can do to remove the digging instinct from your dog. It is normal for a dog to dig. Your dogs tendency to bury items is a part of its instinct for self preservation.