The two most common types of permanent sheep fencing used among North American sheep producers are probably electrified high tensile fence and field fence.
Electra-netting is probably the most common temporary fencing used.
A five or six strand high tensile electric fence is often the choice of perimeter fencing of large areas for sheep. When using high tensile fence for sheep paying attention to the wire spacing is important.
Fencing companies make a couple different recommendations for wire spacing. The bottom wire is placed at either four or six inches from the ground. The next two or three strands are at six inch intervals and then eight and nine inch intervals for the top strands.
Ranchers can electrify as many of the wires as needed and it's common for either all wires to be electrified or alternate wires (with the non-electrified wires acting as ground wires). Running a ground wire setup will net more charge per wire and alleviate some of the problems with losing electric current on the wire.
Over extensive length, with multiple strands, the miles of wire being electrified can be a drain on the overall voltage of the fence. Sheep will crawl through weakly electrified fences.
When the area to be fenced is not as expansive, field fence is also very common. This type of fence is more challenging to stretch properly. The proper stretching tools are a good investment.
Hinged knot woven wire and fixed knot are the two varieties. The hinged knot stuff is the commonly used sheep fence, available at many livestock and feed supply stores. It is called hinged knot because it hinges (or folds). This fence does stretch and sag over time, with heavy snow loads or if animals push against it frequently.
The fixed knot variety has a tied knot at at every join of vertical and horizontal stays, thus it stays rigid and does not fold so readily. It is more expensive but almost stands itself up and will last longer. It's more commonly found with suppliers who deal in game fencing. There are various heights available, saving on cost that way.
Many small scale producers go with some variety of field fence as they are not fencing great distances and can have a secure fence without having any electric fencing to monitor.
If needed, an offset electrified high tensile wire can easily be added to woven wire fence for various uses.
Field fence works decently for keeping sheep and guardian dogs securely within the boundaries and predators out, although the most determined individuals will still find a way in or out.
We are in the process of redoing our entire perimeter fence so I can say with some amount of experience that it's worth it to just go with the best fence available from the start, and not the cheapest. Our new perimeter fence is fixed knot woven wire.
Barbed wire is not recommended material for sheep fencing. The barbs do little to deter the sheep as they can easily avoid the barbs poking them. The real danger to sheep from a barbed wire fence is the wool becoming tangled on the barbs. The sheep will struggle to disentangle itself yet will only further entangle the wool around the barbs and quickly become stuck fast.
That said, existing barb wire fences have been made useful by placing an offset electric wire or two at the appropriate heights to catch a grazing forehead or sniffing nose.
In areas where the sheep are corralled a wooden slab fence probably works the best. Many cattle corrals can be adjusted to suit sheep, the main adjustment being plugging any gaps and holes sheep may fit through. One thing to watch for is the spacing between the slabs. In a high pressure area if sheep think they can get their head through, they'll try.
Electric netting is the wonder of portable fencing for sheep producers. It does work great as temporary cross fencing. Having some of this on hand is a worthwhile investment. It is easily set up and taken down by one person. Individual roles can be carried under the arm. It can be electrified and it keeps animals in and keeps predators out.
The two downfalls of the electric netting are 1) persistent animals and snoopy lambs can become tangled in it. When we are using it we make a regular habit of checking the fence line. 2) If you have particularly hard or stony ground you will fight trying to push the pole spikes into the ground.
Some producers are making good use of two strand high tensile electric fence as temporary sheep fencing. This has proven successful provided there is enough food on the ground to keep them eating and it allows cattle producers to run sheep without adding to their fence costs.