My "perpetual spinach" has made it through the winter on an open meadow site where I have not actually seen rabbits but they are likely to be there (and for some reason my horseradish is the most nibbled by something, but the spinach looks good).
If you sow a long enough row of almost anything you will get a crop. What is a "secure box"? Any form of protection such as netting floated over the row would protect it, but I suspect you won't need it. What you might like is "spinach beet", "bright lights", "chard", "Swiss chard" and so on. They could be about 18" tall. True spinach is almost flat on the ground.