What Base should I use in the Guinea pig / rabbit hutch to stop them from digging their way out?

I have a large cage with two guinea pigs and one rabbit. it has a bare base where they run around on the gr. I suspect the rabbit has been digging the holes under the cage the holes were big enough for my piggies to escape. I want to put a base on it but still have gr exposed so they can eat and i have heard wire is not good for the guinea pigs. Any suggestions on how i can modify the cage to combat this problem.