Notural Organic Lawn Care
If I ruled the world, there would only be an occasional tiny patch of lawn on a property, merely to provide a bit of contrast to the rest of the landscape. In the meantime, people have large lawns that require copious amounts of care, or, at the minimum, serious amounts of fossil fuels to keep them at an agreeable length. For those who both have large lawns and care about the planet, The Ohio State University has a superb Cooperative Extension bulletin, Natural Organic Lawn Care for Ohio. The information works just fine for other states.
Tool or Gardening Product
On the sliding scale of deer invasion, if you live in an area that doesn't require fencing but does get deer damage, start using deer repellents in early spring to keep them from starting in on those first tender shoots. There are a number of deer repellents available, each claiming to be the best. Several universities have conducted studies as well. Most are based on rotten eggs, garlic, and hot pepper. They generally work pretty well, but they do need to be reapplied with varying frequency.