When sprays and gadgets just aren’t keeping the wildlife at a distance, gardeners can find a durable and permanent method for preventing hungry critters from decimating the vegetable garden.

Although the initial cost to buy and build an electric fence is more, the rewards of years of low-maintenance and high efficiency can make the investment worthwhile.

To deliver an effective shock the fence requires a good power supply, grounding and design. Power for an electric fence is measured in joules, rather than watts or volts. The total number of joules required depends on the length of the fence, the number of wires and the soil conditions.

Assuming the fence will be square or rectangular, start by measuring the length of all four sides and totaling the results. If, for example, two sides are 100 feet and two are 125 feet, the initial total will be 450 feet, then multiply that total by the number of vertical rows to be installed. Four runs of wire at 450 feet per run means the total fence project will require 1,800 feet. Plan to purchase extra wire and parts for any unexpected needs.

“There’s nothing worse than having one critical piece getting lost in the deep grass or breaking when you’re almost finished and the store is closed,” said Campbell’s True Value site manager John Smith. “And you’ll have future maintenance and replacement needs, so those extra materials won’t go to waste.”

A fence’s power source can come from a standard home outlet, a stand-alone battery or a solar-powered unit. These fence energizers differ in the size and the duration of the pulses of electrons they send into the fence line.

Larry Donald, manager of Farmington Farmer’s Union, and his staff help customers sort out the many choices and decisions that need to be made before installing an electric fence. After gathering important information about the terrain, the animals to be kept in or out and the size of the property to be enclosed, they can put together a complete package of electric fencing materials.

“Don’t skimp on a quality energizer,” advised Donald.

A good energy source, whether from the sun, an electrical outlet, or a battery, provides a jolt that shouldn’t last for more than 0.0003 seconds. These short pulses keep heat and sparks from building up in the wire and creating a risk for a grass fire in dry conditions. A wire that is too hot also will wear out more quickly. High voltage energizers with long pulses leak the excess electricity, while better-quality low impedance energizers resist leakage. Look for an Underwriters Laboratories (U/L) or Canadian Standards Association (CSA) label to be sure the energy unit meets quality testing standards.

A high-quality insulated grounded extension cord running from a grounded outdoor electrical outlet will deliver a 110- or 220-volt charge and cost a few dollars a month. For larger gardens and those further from an outlet, battery- powered energizers are a practical alternative. Dry cell batteries can power portable energizers, but they have to be recharged regularly and replaced. In permanent installations, a solar battery system is more expensive to buy, but in the long run, there’s no monthly cost or recharging. Deep cycle batteries can be completely discharged and recharged repeatedly. Conventional car batteries can’t be totally discharged and will only recharge up to about 60 to 75 percent of their original capacity. Check the battery’s guarantee for length of time and features covered.

“Don’t buy on price alone,” said Franklin County Cooperative Extension expert Dave Fuller. “The energizer with the cheapest price generally turns out to be the most expensive to run and maintain.”

Buying more joule capacity than currently needed will provide flexibility to charge additional or expanded fencing without having to buy an additional unit. Plan to install posts every 10 to 20 feet, using material that won’t rot when the ground is wet. Holes can be dug with a power auger, which will allow the several feet of depth that ensures adequate grounding and stability. Grounding the system is a critical step.

“Poor grounding is the leading cause of electric fence problems,” said Fuller.

Electrical current follows the wire to and from the energizer. If an animal or a blade of grass touches the wire, the current goes through that blockage into the ground and the grounding rods. Moist soil is a good conductor of electricity, but when it’s dry or frozen, animals will not be shocked unless ground wires are included on the fence.

A minimum of three ground rods should be used for single-energizer fences; a smaller one-joule unit needs only one rod. Use six-foot lengths of 5/8-inch diameter galvanized steel rods or 3/4-inch galvanized pipe. Leave each with six inches above the ground, and space rods at least ten feet apart. Add extra ground rods in dry areas. Fence plans also should include a way to handle a lightning strike. The easiest step is to unplug the energizer during an electrical storm, but consider adding a lightning diverter.