Well unless you know what's doing the damage it will be hard to protect the plant. Leaf damage could be caused by an insect or mammal such as a rabbit or chipmunk. For every pest, there's a different treatment. If you suspect it's an insect, you can try spraying with an insecticidal soap (you can purchase at garden centers or home stores) or if you think it might be a caterpillar then use Bt a natural bacterium that will kill these pests, but not be harmful on vegetable crops. If you think it's a mammal you can screen the plant with chicken wire or use a liquid repellent around the plant. Liquid Fence sells a number of repellents you will also find at your local store. I just can't help without knowing the identity of your pest."