As someone else said earlier in the thread, I fence my garden and let the chickens have everything else. I have a huge garden 'pasture' that I used to plant in, but it was just far too much to keep up with. Now I have a large, fenced, raised bed garden that is just a dream to work in. I love it.
I keep the garden gate open during the off season so that the chickens can go work through it at-will, but it stays closed when I've got seedlings coming up. Once the plants are established, the chickens are allowed back in whenever they want. Any plants that they show interest in, I fence off with hardware cloth.
Last year they discovered my crookneck squash and helped themselves to quite a few before I realized it and fenced it off, but they left the tomatoes and everything else alone for the most part.
I could leave the garden gate closed the entire growing season, but really, it's so entertaining to see the girls browsing around and getting so excited when they find a bug. They still holler like they've won the jackpot when they find one and then tear off like their tails on fire with the rest of the girls in hot pursuit, just like when they were little peeps!
So, for me, the entertainment and laughs are very much worth the random squash-donation.