What's eating the tomatoes off my plant, and how do I stop it?

ARGH! I’m trying to grow tomatoes for the first time, and I have 3 plants in pots on my deck. I was SO excited because the first large tomato was getting ready to pick, and I walk out this morning to give the plants water and more than half the tomato is gone! Something clearly came and took several large bites out of the tomato. This is the second time this has happened, although the first time it was less clear that it was a bite, I thought the fruit was maybe just damaged.

What’s eating them, and how do I stop it? I’m thinking maybe a raccoon? Would anything else do this? I don’t think we have squirrels here, I’ve never seen any. Would a motion-sensitive light work to deter the animal? Any other techniques?