There are several ways to repel flies outside, including:

1. Scents: Flies are particularly opposed to strong, pungent odors like clove, lavender, mint, lemongrass, eucalyptus, rosemary, and citronella.

2. Fly-repellent plants: Several plants can help keep your yard free from pests, such as lavender, peppermint, marigolds, basil, and rosemary.

3. Cleanliness: Flies are attracted to waste, so its important to keep your yard well-maintained and remove waste, including pet waste, overgrown grasses, and rotting plant matter.

4. Fans: Using fans can make it difficult for flies to fly, and they can be used as a deterrent.

5. Light-based fly traps: Flies are naturally attracted to bright lights, so using a light-based fly trap can be a great way to clear the yard.

6. DIY fly repellent spray: In a bowl, mix 1 cup of water, 1 tablespoon of vinegar, and a few drops of dish soap. Spray around the home to deter flies.

7. Pennies in a glass of water: Putting pennies in a glass of water can also repel flies. The water and pennies create a prism that reflects colors, which flies dont like.

Its important to note that while natural fly deterrents can be effective, they may not be as effective as using a fly swatter or commercial insect repellents.