Deer are edge species, meaning they spend much of their time on the perimeter of forests and tree stands. There are two primary reasons for this. First, deer like to eat the young supple shoots and sprouts that are found at the perimeter of forests. In the middle of an old growth forest, there's just not enough light for saplings and other lush plants to grow. So, when we clear the land where the larger older trees once grew, younger sexier trees are able to grab some light and sprout up. This new growth provides ample nutrition for the darling little deer. The second reason is safety. When the deer are munchin' away on baby aspen, balsam or your ornamental plants and shrubs, they can make a quick escape into the dense woods if danger arrives. So you can see why a yard surrounded by trees is a pretty exceptional place to be; there is food within reach and cover nearby.
Put up a fence. And not just any fence. Deer are jumping machines. This thing needs to reach the sky. You'll be looking at 8-10ft high with at least one foot buried underground. If the idea of the Great Wall of China in your back yard doesn't appeal to you, you can also try using an electric fence baited with peanut butter. A little zap teaches a quick lesson. Just be careful when using electric fences that dogs, cats, children etc. don't inadvertently get shocked.
Place tubes around the base of trees. Not only will this protect the little trees from getting munched on, but in the fall, when deer are trying to shed their antlers, they rub them vigorously against the trunks of trees. While this works well for the deer in working those antlers loose, it wreaks havoc on tree bark and can lead to stunted growth or even the death of the tree. Many commercial tree protectors are available, or you can simply make your own by slicing some corrugated drain pipe lengthwise and wrapping it around the tree trunk.
Protect plants with row covers. There are several types of row covers, some are light weight enough to just be draped over your plants while others are designed to be suspended by hoops or stakes. All designs help to keep deer and other pests from devouring your gardens and plants. They have the added benefit of providing some protection against frost (usually just a couple degrees) and retaining a little extra moisture for the plants use
Erect small cages around vulnerable plants, shrubs and bushes. By using small cages, either homemade with stakes, fencing or chicken wire, or commercially purchased, the deer will never even know what they're missing. If they've already munched your plant a bit and you're providing protection after the fact, make sure to secure the cage to the ground around the plant with some good long tent stakes Otherwise the deer will just push it over or toss it aside when they come back.
Don't feed other animals. Deer love a free handout. They are quite often found grazing seed from underneath birdfeeders. They've even been known to grab a birdfeeder with their mouth and tilt it so all that tasty sunflower seed spills to the ground for them to eat. If you have corn out for ducks, turkeys, pheasants, quail or whatever, you will also probably end up with deer.
There are three main types of deer repellents: area repellents, contact repellents and electronic repellents. Below you will find several examples of each and a short explanation (as that's all that's needed) on how to use each type. I've been told over and again that the most important thing to remember when trying to repel deer is to switch things up on a regular basis. Deer have more than a couple brain cells and quickly become used to and undeterred by the same old repellent. Some people switch back and forth with a couple different products every few weeks and other folks use a constant rotation of three or more.
Area Deer Repellents. Area repellents come in liquid, powder or granular form, are applied around problem areas and repel deer with foul odors. A deer's sense of smell is far more sensitive than a human's, so something that smells slightly bad to us could smell absolutely putrid to a deer. Examples are Deer Scram, Shake Away, Liquid Fence, Milorganite Fertilizer (though I've heard it can't be sold as an area repellent) and predator urine from coyotes, mountain lions, bobcats etc.
Contact Deer Repellents. Contact repellents are generally liquid, applied by spraying directly onto the plants and taste and smell terrible to deer. Examples are Deer Away, Scoot Deer, Miller's Hot Sauce, Deer Off, Hinder and predator urine.
Electronic Deer Repellents. Electronic repellents are attached to an object such as a stake or tree in the problem areas and generally work by irritating, scaring or startling the deer. YardGard Electronic Deer Repeller and DeerGard Silent Deer Repeller both emit sonic and ultrasonic sound, are motion activated or can be set to run continuously. Deer Chaser is a motion sensitive device that uses a very bright LED light and an FM radio to scare deer away.