Back in 2003 I have a 5 foot red/black retaining wall built in my back yard. In the middle of this wall the contractor built 7 stairs out of the pavers and packed down behind each set of stept. A 4 inch thick concrete patio was laid over the top of of the wall and steps. However, in the last 2 years I have noticed that the top 3 rows of steps have concaved a bit leaving a 2-3" gap just underneath the poured concrete. The stairs are still very sturdy but I am at a loss as to what to do about the problem. There are garter snakes living underneath and there are several holes around as the neighboring wall is made out of broken concrete slabs. I have no dirt or mud run off onto the steps, just the settleing. What can I do to fix this so the cement slab won't crack?