There are a number of products available that repel biting flies and mosquitoes away from people. I do not recommend the use of one product over any other products. I do not work with biting flies or mosquitoes; therefore, I am unsure how effective most 'natural' repellents are at keeping biting insects away. I generally do not have many issues with biting insects and when I do, I use any of the commonly available deet-containing products. There have been new products that use a battery powered fan clipped to a belt in order to mist the area around the wearer with a repellent and I had some success with it a few years ago, but no official experimentation was conducted with the product.
Deer flies, biting midges, no-see-ums, and other gnats often require saturated soils with high organic matter or water for successful larva development. Applications of insecticides to lawns or trees and shrubs in a landscape to reduce nuisance/biting insect populations is not cost effective for an individual homeowner. Communities often may employ a professional to mist large areas to manage outbreaks of flying biting insects but what they use and what level of insect infestation is required for treatments to occur-- I do not know.