Deer will ransack a garden when you're not looking. They will leave behind trampled plants and eat the produce with no regard for your hard work. To keep deer away from your tomato plants and other garden veggies, you can go with a simplistic covering or a more expensive overall fencing. Either way, once you are done, you will have one less pest to worry about.
Cover potted tomato plants with a cloth like tulle. It has many holes, which allows in light, rain water and air so that the plant can get everything it needs to grow, but it prevents animals from getting to the plants. The airy quality of the tulle will also insure that mildew doesn't form from trapped moisture, and the cloth is lightweight, so it won't weigh down the stems.
Install fencing around large gardens of vegetables like tomatoes. It is possible to cover each plant with tulle, but this can be time consuming if you have a large garden or farm. Fencing will surround the entire area and protect more than just the tomatoes.
Install ultrasonic sound machines. These will emit a sound that deters animals, but cannot be heard by humans. The pitch is too high to register in a person's ears, but animals won't be able to stand the noise. They will avoid the area where the sound is. Barking dog sounds are also a good technique for scaring away deer and other animals.
Grow around your tomatoes other vegetables or plants that give off a strong odor. Herbs are a sure bet, including sage and mint. Peppers will also work well.