Answer: How infuriating! Based on the damage you are describing, I would suspect a four legged animal rather than an insect. Are there deer in your area? If so, I would suspect them. To be sure, you'll need to check outside periodically during the night time hours -- or look for hoof prints. (Another possibility, although a faint one, is a woodchuck.)
Many gardeners report success using the commercially available repellant sprays applied and reapplied according to the label instructions; there are also many home remedies such as soap, human hair, or blood meal sprinkled about the plants. In my experience, though, the only reliable method over time is a fence.
I'm sorry about your plants.
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