raised bed keeping voles out

the voles seem to be everywhere here. and my cat family is down to just 2, momma cat and one of her babies, I lost 4 cats this summer, 1 to a hawk, 1 to coyote, one I have no idea what happened and just this past week 1 to a an unwanted dog someone dumped off on the road.
back to the raised bed. ive got a space picked out and was thinking of a layer of rocks on the bottom and some busted up redimex cement that has been hardening in the bags for a couple years.
has anyone tried anything like this to keep voles from tunneling up into a raised bed garden?

Yours sounds like a reasonable idea.  I was thinking hardware cloth.

I used 1/2" chicken wire to line the bottoms of my beds and stapled it to the insides.  I'm not 100% sure it will keep critters out but it's better than nothing.  I have definitely heard it said, as John just did, that hardware cloth is superior to chicken wire.

Expanded shale (Permatil) advertises that it blocks voles/moles if added to soil. I bought a cubic yard from a landscaping nursery and I use it everywhere since I am trying to break up a lot of clay.

Dennis Bangham wrote:Expanded shale (Permatil) advertises that it blocks voles/moles if added to soil. I bought a cubic yard from a landscaping nursery and I use it everywhere since I am trying to break up a lot of clay.

Dennis, are you seeing any improvements after using the expanded shale? I'm wondering if fine crushed rock chips would also work, as that is readily available where I am.