You have a couple of options. Dogs can be chained along boundaries of crop fields or near gardens to deter jackrabbits.
Repellents
Since state pesticide registrations vary, check with your local Cooperative Extension or USDA-APHIS-Wildlife Services office for information on repellents legal in your area. Various chemical repellents are offered as a means of reducing or preventing hare damage to trees, vines, or farm and garden crops. Repellents make protected plants distasteful to jackrabbits. A satisfactory repellent must also be noninjurious to plants.
In the past, a variety of repellents have been recommended in the form of paints, smears, or sprays. Many of these afford only temporary protection and must be reapplied too often to warrant their use. Other more persistent materials have injured the treated plants. Some chemical substances such as lime-sulphur, copper carbonate, and asphalt emulsions have provided a certain amount of protection and were harmless to the plants. These are less commonly used today and have been replaced by various commercial preparations such as ammonium soaps, capsaicin, dried blood, napthalene, thiram, tobacco dust, and ziram, which are probably more effective. Repellents are applied during either the winter dormant season or summer growing season. Recommendations vary accordingly. Be sure to use repellents according to the manufacturer’s guidelines and follow label recommendations.
Powders: Any repellent applications that involve the use of powders should be dusted on garden crops early in the morning, when plants are covered with dew, or immediately after a rain. Do not touch plants with equipment or clothing because moist plants, especially beans, are susceptible to disease. When a duster is not available and only a few plants are involved, use a bag made of cheesecloth to sift repellent dust onto plant foliage. Repeated applications may be necessary after rains have washed the powder from the foliage and as new plant growth takes place.
Sprays: Thoroughly cover the upper surfaces of the leaves with spray repellent. If a sprayer is unavailable and only a small number of plants are involved, a whisk broom or brush can be used to apply the repellent to the plant foliage. The repellents will adhere to the foliage for a longer period if a latex-type adhesive is used. Re-apply liquid repellents after a heavy rain and at 10-day intervals to make certain new plant growth is protected.
Some repellents are not registered for application to leaves, stems, or fruits of plants to be harvested for human use. A list of registered commercial repellents can be found in the links below. Many of these may be purchased at a reasonable cost from suppliers handling seed, insecticides, hardware, and farm equipment.
Commercial repellents containing thiram are effective and can be applied safely to trees and shrubs. Treat all stems and low branches to a point higher than rabbits can reach while standing on top of the estimated snow cover. One application made during a warm, dry day in late fall should suffice for the entire dormant season. Coal tar, pine tar, tar paper, and oils have caused damage to young trees under certain conditions. Carbolic acid and other volatile compounds have proved effective for only short periods. For further information on repellents and their availability, visit the Web site referenced below.
Resources: (online)
Jackrabbits
Supplies
