Landscaping - Replace wood around Patio w/ landscaping stones

I am wanting to replace the wood around my patio w/ landscaping stones. I started removing the wood because it was rotten and found that there were some gaps under the the patio. I want to somehow back fill the holes under the patio so that it doesn't collapse or break. What is the best way to do this? Any Ideas?

It sounds as if the patio has settled and you need to add more sand/limestone underneath to shore it up. I would try to push it under there, then also go over the top of the patio with a round of sand so it goes down in the cracks from the top. Lightly mist the sand and sweep it across. Wait a few days and then check it again to see if there are more holes. Once you think it's all filled, add the stones you want around the edges.