The University of California Division of Agriculture & Natural Resources provides excellent information regarding the identification and life cycles of deer. "Deer can be very destructive to gardens, orchards, and landscaped areas, particularly in foothill and coastal districts where nearby woodlands provide cover. Mule deer, Odocoileus hemionus, and blacktailed deer, O. hemionus columbianus, are the two most common subspecies in California." ( T. P. Salmon et. al., 2004)
Various chemical repellents are sold for reducing or preventing deer damage to trees, vines, and ornamentals, although their effectiveness in most situations is not very good or long lasting. Deer repellents are designed to impart objectionable odors or tastes. Most are not allowed on food crops, so if that is its intended use, make sure the repellent is registered for that purpose. When deer are hungry and a garden area contains highly preferred foods, repellents are much less likely to be effective. It is important to remember that some repellents can be injurious to certain trees or shrubs, especially to the new growth. If in doubt, test the repellent on a single plant to make sure it is not phytotoxic (harmful to the plant). When you use deer repellents, follow product label directions carefully.
Most repellents should be applied before damage occurs and must be reapplied frequently, especially after a rain, heavy dew, or sprinkler irrigation. Likewise, to be effective repellents must usually be applied to new foliage as it develops. Some repellents produce odors thought to frighten or repel deer from an area. Examples are human hair, soap bars with an intense aroma, and mountain lion urine or other types of predator odors available commercially. Although these substances may repel deer for a day or two, they have not proven to be satisfactory in protecting gardens from deer damage in California. (Deer Management Guidelines - UC IPM)
MECHANICAL AND PHYSICAL CONTROLS
"Deterrents such as fences, barriers, frightening devices, and various repellents are recommended and can all be used without a permit. Physical exclusion is by far the best and most reliable way to protect gardens, orchards, and ornamental plantings from deer." ( T. P. Salmon et. al., 2004)