I don't know what the rules are for your science fair, but for ours, we had to follow the Scientific Method and everything. So we had to have a hypothesis of what would happen and a reason to back it up. We also had to be able to quantify our results; that is, they had to be something measurable. Are you required to have controls? To me, just burying some bones and digging them up later sounds cool, but doesn't really tell you a lot. And it's hard to quantify that if your school requires measurements. It might be more informative if you split the bones up and then did different things with them. (For example, bury one set, leave one set submerged in water, leave one set out in the open, etc.) Then you could compare and contrast the different sets. Good luck!
Yes bury it in a fertal area and let it decompose then dig it up.