Rabbit Burrowing question?

I've noticed that my my male rabbit, Bruno, likes to burrow in our little sand area and then lay down in it.. His new hutch is located in that area and we are going to soon make access to the bottom so he can eat gr/ be in the sand to cool down. The only think is, is that I dont want him to burrow and get out. I'm alright if he burrows, but I know placing anything above ground wont stop him from getting out.. Do you think i can put cement blocks under the base of the hutch so he can burrow but he cant get out because the cement will stop him? Let me know, thanks! :)