Natural England provide guidance on the construction of beaver fences. Although this guidance is a basic blueprint, each experience will suggest modifications on the grounds of practicality and expense. The fence style outlined below has been developed from recent experience of two projects in Devon. Beavers are excellent burrowers in friable soils so underground fences which do not extend beneath the normal water table must normally be set well back from the waters edge (more than 30 m). Where the fencing can be set over 30 m away from any friable bank side habitat then a perimeter fence can be erected with a collar facing inwards at a 90 degree angle. The collar at ground level should be extended into the enclosure to depth of 45 inches and pegged into the ground. Vegetation will grow through this rapidly ensuring that it forms an extremely secure mat. Experience gained in Bavaria from holding large numbers of beavers over a 10 year period in small temporary enclosures indicates that adult beavers are very poor climbers. To counteract this ability in England, beaver fences have traditionally incorporated main or solar powered hotwires at heights of typically 38 cm and 75 – 100 cm as internal components. Shortage of power from these fences due to vegetation is problematic – lower electric wires are particularly difficult to maintain as these realistically can only be kept clear with herbicide, flame throwers, geo-textiles or salt – and experience gained recently from three separate holding facilities where beavers died as a result of gripping the medium wire in their teeth suggests that this design is hazardous. A better solution may be to employ an anti climb strip of smooth material (tin or fibre glass) attached to the top of the fence by hog rings. This was historically a standard method of containment on mink farms for a much more agile species. It should work well with beavers.
A recommended design for beaver fencing is outlined below. This consists of 7 ft (2.13 m) ‘cundy’ peeled posts set on the outside of the fence – opposite to the beavers – sunk 90 cm into the ground and standing 1.2 m above the surface. Three inch (7.6 cm) squared high tensile wire at a height of 1.2 m is strained across the posts. At a height of 90 cm and a 30 cm broad strip of smooth fibre glass or sheet tin is hog ringed to the internal wire. Along the base of the fence a 2 inch (5 cm) weld mesh curtain extends into the enclosure for 90 cm. This curtain extends up the perimeter fence to a height of 30 cm and is hog ringed to the fence. Where straining posts are set on the internal side of the fence these must be protected with 2 inch weld mesh guards. If burrowing is perceived to be an issue then this basic fence can be adapted by extending a 2 inch weld mesh curtain extends down into the ground to a depth of 1.2 m.