I use fill dirt on top of the concrete, and then add straw...it's working for me and it seems to have made my coop warmer since before I just had shavings on top of the concrete.
Picture of your coop?
I used wide pieces of wood and then concrete blocks on top of that but my coop was inside a barn and the wood did not get wet.
I had raccoons that used a tunnel made by a groundhog to get into my coops.