It's most likely rabbits, I've not heard of squirrels eating plants. There are several commercial products available that you spray on the plants to deter the little buggers. One that I've heard good reports on is Plantskyd. There are several others that work fairly well too, just can't remember the names at the moment. You do have to reapply them. They should be available at most garden centers.

I use repels all for deer and rabbits. They don't eat my lilies but do eat daylilies and other tender plants. I buy it at Lowe's. Now if I could just get rid of the moles. grrrr