We have a 4 foot concrete border/deck that surrounds our pool which is then surrounded by our lawn. Late last year I saw both a racoon and a rabbit disappear into an opening where the lawn met the concrete border. At the time I thought they had dug out a bit of earth from under the concrete border and were using that area for shelter.
Fast forward to today and I finally decided to see if I could fill in these two openings and see if they did any damage. However, after digging a trench along one side of the concrete border and looking underneath I discovered there is about a half foot opening from the bottom of the concrete to the earth below it that extends most of the way around the pool. I'm assuming the earth settled this far down since the original owner had the pool built, but now I'm not sure what I should do. Is this something that people live with or do they fill in that gap if it develops over time. If so, what would I use to fill it in (soil, sand, stone etc)?
Here are some pics that give a better idea of what it looks like:
Here's the concrete border:
This is the trench I dug so I could see under the concrete:
Here is the gap under the concrete showing the pool wall at the back, the concrete/stone mixture on top and the earth on the bottom:
Another view of the gap: