I have attributed a lot of things to deer, when it was the
rabbits that were eating the plants, or packrats that were chewing off stems and leaves for nesting material. The only thing that stops any of these is a
chicken wire
fence, 8 feet high to keep the deer out, bent outward at the bottom at least 6 inches and held down by letting the grass grow through it. Even then, clever birds see colorful tomatoes and apples and pears and help themselves.
But, for nitrogen fixing for summer growth, a mixture of field peas, beans and clovers will not only fix nitrogen, but their foliage can be mowed or chopped finely and left as mulch. Let some of them re-seed for late summer growth. I've found these mixes at nurseries.
The most reliable natural source is look around your own area for nitrogen fixers already growing there and get the seeds or transplant the native ones. Vetch is pretty common, has pink flowers. Those are most likely critter resistant and will suit your climate.
An important distinction: Permaculture is not the same kind of gardening as organic gardening.
Mediterranean climate hugel trenches, fabuluous clay soil high in nutrients, self-watering containers with hugel layers, keyhole composting with low hugel raised beds, thick Back to Eden Wood chips mulch (distinguished from Bark chips), using as many native plants as possible....all drought tolerant.