Oooohhh, the Fluffy-Tailed Rats.
A plague on the earth (literally: in California, at least, these...creatures...can carry Yersenia pestis
, also known as bubonic plague).
The Sunset Western Garden Problem Solver
(a different book from the one I usually recommend) shows a photo of a protected raised bed using "aviary wire." It looks like chicken wire, but with much smaller apertures. Might be equivalent to half-inch hardware cloth, but there's no scale on the photo, which shows the aviary wire covering the bottom and sides of the box. It's just bent, gently, at the "seam." My copy of the Problem Solver
was copyrighted in 1998 (although I'm pretty sure I purchased it in 2008), and the photo is on page 44. This method of protection is suggested explicitly for gophers and rabbits (well, some reading between the lines re. rabbits).
Sunset, in 1998 at least, didn't seem to realize that squirrels will attack our veggie plants.
The only--and I mean only
--recommendation in this section on "Avoiding animal damage" that relates to Fluffy-Tailed Rats (aka squirrels) discusses the need to put out "bird feeders...that work fairly well to keep out all but the most persistent squirrels. If squirrels are burying nuts in your container plants--a favorite storage space [they buried empty peanut shells in my beds
]--try using small red lava rock as a mulch. Its coarse surface acts as a deterrent" (p. 45).
Talk about useless
advice! Lava rock, once in the soil, is almost impossible to deal with. When you want to mix in additional compost, guess what? ==> The lava rock is in the way and needs to be either hand-picked out or sifted out. Bleah.
This, IMHO, is the place for chicken wire; it'll make digging in the soil unpleasant, both for squirrels and for any cats that may view the veggie container as a very large, comfy kitty box.
To protect the veggie plants themselves, I think rainbowgardener ties up deer netting on the raised beds.