The effectiveness of predator-resistant fencing is influenced by a variety of factors, including the density, age and behavior of local mountain lions, the terrain and vegetative conditions, the availability of prey, size of pastures, season of the year, design of the fence, quality of construction, and maintenance concerns.
Properly built electric and non-electric fences have prevented or significantly reduced how often mountain lions prey on livestock. Fences are often used to habituate predators to move elsewhere in search of prey, because fencing is so costly to completely exclude them.
Mountain lions can leap a ten foot fence with ease, so fences should be at least 12 feet high.
The best materials will be difficult for a lion to climb, such as heavy woven wire or chain link.
Fences constructed to keep Florida panthers off the highways have also included a broad wire mesh overhang at the top of the fence to prevent lions from climbing over.
Whatever kind of fence is used, it is important to be vigilant about clearing overhanging tree branches as well.
Section 5.3.2 of the Federal Highway Administration's Best Practices Manual: Wildlife Vehicle Collision Reduction Study shows photographs of the fencing used to prevent endangered Florida Panthers from crossing freeways. Only the highest and best constructed fences have proved effective.
Some property owners have achieved better protection by using alternating hot and grounded electric wires on their fencing. However, given that a mountain lion may be able to clear a ten-foot fence without touching it, the electric charge on a typical low-hung three-wire fence will not be much of a deterrent. To complicate matters, a lion's fur coat provides some insulation from electric shock, requiring relatively higher voltage to be effective, and increasing the risk of electric shock for other wildlife, people and pets.
Adding one or more electric wires at the top of a 12 foot chain link fence may help to prevent lions from climbing over, and perhaps reduce the risk.
One example of a low-cost fence that solved a mountain lion problem in Montana can be found on page 109 of the Living with Predators Resource Guide (17MB pdf file) provided by the Living with Wildlife Foundation.
When a pen or barn is not feasible, you might consider fencing a smaller area in which to confine livestock at between dusk and dawn, Similarly, temporary fences may be used to confine young domestic animals for the first month or so after birth, when they are particularly vulnerable. Injured or sick animals can also be fenced in and away from the rest of a herd, since the scent of blood or illness may attract predators.
While permanent fencing may help protect small pastures or backyards, it is too costly and impractical for the vast public lands of the west. Temporary or portable fencing can be used to keep livestock together so that herds can be guarded more effectively. Portable electric fencing is easy to set up and far less expensive than the permanent predator-resistant fences described above.
An electric fence is not a physical barrier: it's psychological. Herd animals must be trained to fear the fence, and should never be confined within when the voltage is too weak or the fence is turned off. It's the same for predators: the initial (and repeated) shock from an electric fence may train them to return to the wild in search prey, even though the fence itself might be easily breached.
Because the fencing is a psychological barrier, it must be visible. White wires are more visible than any other color against most dry or lush grassland backgrounds. Mountain lions do not see color as well as high contrast, so white wiring will be more effective than red, orange or yellow.
Dry soils can prove to be a big problem for temporary electric fencing. Grounding rods require damp soil, and may disable the electric current when the earth retains little moisture.
Some good general guidelines about temporary electric fencing can be found in Fences that Work.
The benefits of temporary fencing can be improved when used in conjunction with shepherds or guard animals. Temporary fencing has additional advantages, including greater control of grazing, reducing impacts on vegetation, eliminating the need for herding, and avoiding parasitic infestations by minimizing contact with adjacent herds.
A significant downside to using preventative fencing to divert mountain lions is that should a lion inadvertantly become enclosed in an area with prey with no easy and apparent exit, the lion will kill — and continue to kill — until all movement has stopped.
This is instinctual, not a choice or decision. It is not done because lions are particularly cruel or wasteful. The basis of this behavior is that lions hunt herd animals, and their experience is that once one animal has been taken, the others will surely flee. When this does not happen, it is an unnatural event, and the lion perceives danger. If escape is not easily achieved, or the lion does not remember how he entered, it will kill again.
Mountain lions are vulnerable to infection and death from even the slightest injury, and are often injured by their prey, even when only confronting a single animal. So killing any and all immediate and evident threats provides safety to the individual and an evolutionary advantage to the species. Moreover, mountain lions cannot distinguish detail or color as we do, and rely more specifically on movement, sound and scent to determine the level of danger.
There is no easy answer to this dilemma, but it's important to understand the issue when making a choice about using fencing rather than total exclusion and enclosure.
Coyotes, wolves, foxes, dogs and skunks will dig beneath even the strongest fence, so be sure to bury the bottom of the fence. We recommend placing fencing material along the ground that extends out a few feet to create a buried apron or skirt along the entire width. Attach it to the fence, stake it down, and bury it 6 to 8 inches from the surface. This feature capitalizes on canines' instinct to dig at the base of a wall.
Many additional resources have been detailed for protection from bears, which use their great strength, persistence and dexterity to break into many an enclosure that would thwart a lion or coyote. We suggest reading Electric Fencing for Bears by the Virginia Department of Game and Inland Fisheries and Bears and Electric Fencing by the Montana Fish, Wildlife and Parks Department,
Please keep in mind that fences (or other man-made obstacles such as homes, businesses, roads, or domestic grazing operations!) should not be placed where they will block important migration corridors for scarce, threatened or endangered wildlife. Inviting deer into your backyard or pasture is generally not a good idea — as predators will almost certainly follow — but check with a local biologist to ask whether your property is part of an irreplaceable wildlife corridor if you are uncertain, and before you build your fence. For more information about wildlife corridors, be sure to listen to the audio feature highlighted below.