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Use flashing lights or loud noises to startle deer. Set up a motion-activated sprinkler system that will spray deer. Let your dog out in the yard or set up a dog decoy if you don't have a pet.
Blow a horn or whistle or blink a flashlight if you see deer in your yard. You can also get sensors that emit high-pitched noises when they detect movement. Keep in mind you will need to change your method at least every 3 weeks as deer will quickly adjust to any 1 method.  For example, if you're using a whistle, after 3 weeks, switch to the flashlight. Try hanging old CDs or aluminum foil from trees or shrubs. The flashing lights from the CDs and rustling noise of the foil help deter deer. Wind chimes rattling in the breeze or a flashy garden accessory with moving parts like a pinwheel are both decorative ways to keep deer away. These sprinklers go off when they detect any movement, like a deer stepping into your garden. Place them anywhere you don't want deer. However, the sprinklers only work in the warmer summer months because they'll freeze up in the winter.  Look for a sprinkler with an infrared sensor that will detect motion at night, too. Move your sprinkler around every couple of weeks so the deer don't become used to it or learn how to avoid it. Deer are afraid of predators like dogs and are likely to steer clear if they suspect one is nearby. Keep Fido outside more often or stake a silhouette of a dog in the yard. Even the decoy will frighten deer.  Scattering dog hair on the ground around specific plants and trees or around the perimeter of your garden gives off the scent of a predator to deer, scaring them off. Decoys of any predators, like owls, coyotes, or hawks, will work. You can buy decoys that move, too, which are even more effective. Keep your dog's safety in mind. Don't leave your dog outside if it's raining or really cold. Smaller dogs shouldn't be left unsupervised for long periods of time, either, if there are birds of prey in your area.