For the most part, alliums themselves are rodent resistant because of their onion scented bulbs and foliages. And, given that squirrels have a very sensitive sense of smell (they can smell a fresh load in my bird feeders a mile away!) it may be enough to stifle them a bit. I haven't had any trouble with my alliums, but other spring flowering bulbs (especially crocus) get dug up and munched. I don't have them planted close to one another, though.
hortster