There are many kinds of electric fences directed against deer, and they have many different uses. The simplest merely seek to keep occasionally browsing deer out of summer gardens. They have one wire, at a height of about 3 feet, and typically feature baits that draw the neighborhood deer, shock them, and train them away from the protected garden before anything really tasty emerges. Typical materials for such a fence include a fence charger (also called an energizer); insulated hookup wire; metal wire or polywire mounted on insulators and fiberglass posts; metal posts supplementing the fiberglass line posts at gates, ends, and corners; gate and corner accessories; and a ground rod wired to the charger's negative terminal.
Fences for More Deer, Larger Areas
But what if you have more than occasional interlopers? What if you have a small herd threatening your garden? What if you want to protect a larger area? Or what if you want to protect your landscape plantings in winter when deer are starving and highly motivated to intrude? In all these cases you are likely to need something more than a simple one-wire electric fence. You could of course put more charged wires on the fence to discourage deer from jumping the fence or nosing under it. That would help all right; but a better solution is to add a second line of posts three feet behind the first and to put new metal wires or polywires at heights of about 21 and 48 inches on these new posts. That will have a great deal more deterrent power than just adding new wires.
One reason for the added effectiveness: the inner wires can run quite close to protected shrubs, depriving the deer of any good landing place if they choose to jump the fence; while the outer wire is far enough away from the shrubs to prevent browsing from outside the fence. Another reason: Deer have poor close-in depth perception. Their eyes are on the sides of their heads, so they don't triangulate well. As a result, anything averse (like an electric fence) that has a 3D element makes them wary and far more reluctant to mount a challenge than they would be if the 3D element were missing. Materials for a fence like this are the same as those for the one-wire fence, but one obviously needs more posts, polywire, insulators, and corner and gate accessories.
Dealing with Really Tough Conditions
All good things have their limits, however, and all electric fences that have to deal with parched or deeply frozen soil run into trouble. That's because dry or deeply frozen ground won't carry a charge from the target animal's feet over to the ground rod, and so the animal will fail to get a shock. One can remedy things somewhat by running a heavy wire along the fence line on or just under the ground and connecting this to the charger's negative terminal. Then the charge will only need to travel from the deer's feet over to this wire in order to be sure of administering a shock. A better solution, however, is to run a neutral electric fence wire a few inches away from each charged wire. Be sure to keep these wires out of contact with the charged wires and connect them to the charger's ground terminal. Then the target animal will get a shock whenever it touches a charged wire and a neutral (grounded) wire at the same time, with the charge passing through the animal, into the neutral (grounded) wire, and over to the ground terminal on the charger, thereby completing the circuit.
Beyond this are other problems. If the deer pressure is heavy, one animal-to-fence contact or another is apt to uproot posts, break a wire, or otherwise neutralize the system. Then no deer will get a shock and the whole group is free to enter. It's also possible that the deer will learn how to jump both lines of posts, and the longer the fence the more likely this is to happen. So maintenance problems and jumping problems rise as the fence gets longer, and so does the time needed to periodically refresh the baits every 10 days or so, a task that requires one to visit all the baits along the fence's entire length. Thus, while it is possible to install very long 3D fences, this class of electric fence works best when it is limited to distances of about a quarter-mile.
What this means is that where there are severe grounding problems, or large deer populations, or established deer paths, or a large area to be protected, or commercial crops (vineyards, orchards, etc.) with high value being threatened, it becomes useful to seek more robust answers.
One such answer is a tall (6+ foot) high-tensile electric fence. However, such fences are expensive. Also, they need to have low charged wires; so weeds tend to come up and neutralize the fence, at which point the deer have little trouble getting through. A somewhat more expensive but better alternative if a 3D electric fence won't do is some sort of barrier deer fence.
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Are Electric Deer Fences Safe?
By and large, electric deer fences powered by modern "low impedance" fence chargers are very safe—because the power is only "on" for a few thousandths of each second, and so it is easy for anyone receiving a shock to let go. However, any absolute determination of a fence's safety depends on a number of things—including the nature and power of the charger; the nature of the fence; and the extent to which accidental exposure to the charged wire can be limited.
A good many years ago a fatal injury occurred when a very young child's head came in contact with a high-powered electric fence wire running a few inches off the ground. This was a rare accident, one reportedly involving direct contact with standing water. Nevertheless, it shows that some obvious precautions are justified. These include putting appropriate warning signs on electric fences; keeping infants and pets out of range; warning children to stay away; and in general avoiding accidental human contact with the charged wire—especially contact between the wire and a person's head or neck.
What About Other Deer Control Measures?
Deer repellents offer an alternative that is less expensive (if one does not consider application costs) but also less effective than electric fences. They can sometimes work in the hands of knowledgeable people, but they need to be renewed periodically and also varied every few months to keep the deer from getting used to them. This need for frequent renewal makes repellents highly labor-intensive. Even so, they provide an alternative to electric fencing that deserves consideration.
Several other alternatives take the form of mechanical devices mostly geared to controlling small areas. Leaders among these are noisemakers and water-sprayers, both of which typically have an infra-red or motion detector so that they only go off when triggered by heat (from a warm body) or motion. Aside from controlling very limited areas, these devices' main problem is that the deer get used to them and then side-step or ignore them.
Another limited device is the electrified and baited post. It was found that deer fences generally work (as we have noted) by attracting deer to bait and administering a shock to an exploring nose or tongue. In that case, someone reasoned, why not do away with the electrified wire altogether? Why not simply have a small fence charger built into a baited post, so that the deer get a shock when they touch or explore the bait? The main advantage of this method (doing away with the obtrusive wire or other fence conductor) is also its main disadvantage. That's because once you do away with your conductor, there is nothing to connect the posts. So each post needs to have its own battery and fence charger, which makes the system quite expensive. As long as they are kept in good working order, these posts can probably be quite useful in keeping deer away from small specified areas. And if one wishes to spend enough money and change enough batteries, they can probably deal satisfactorily with low deer pressure over a wide area. Even so, anyone trying to substitute such posts willy-nilly for any significant length of electric deer fence will need deep pockets and is likely to be disappointed.
On the high-end side, barrier fences provide a superior but more expensive alternative. Low baited electric fences usually do a good job dissuading deer, but they certainly are not foolproof. More expensive high-tensile electric fences are not suited to all situations and tend to be porous to the deer. Thus, there are plenty of circumstances where a barrier fence is worth considering.
Can Electric Fences Be Usefully Combined with Other Measures?
They sometimes can. For instance, suppose you already have a barrier fence and would like to improve its deer-repelling power. You can do so by running a low (3-foot) electric fence outside the barrier fence, making it necessary for the deer to confront both fences simultaneously.
Or let's say you plan to put a barrier deer fence across a heavily-traveled deer path. Your chances of successfully interdicting the path are poor; but they can be improved by temporarily installing an electric fence and a motion-activated water sprayer along the path ahead of the fence. That way the deer will have three challenges to deal with, and they will be more likely to abandon the established path.