Some call the 1900s "the century of the barbed wire". Doing it right in 28mm scale has some challanges
A true barbed wire has it's barbs about 1cm long placed 10cm apart. In 28mm scale this translates to 0.2mm and 2mm respectably — any attempt to model them in scale is doomed to fail.
To get some realistically-looking barbed wire you can go two ways: use a simple wire or a pair of twisted wires (as the 0.2 mm barbs are effectively invisible) or purchase a photo-etched wire in a hobby store. The latter wire will have the barbs hugely exaggerated but if someone is not a picky modeler it will do fine and look cool.
Now that we have the wire, we need to set it up. There has been lots of ways to do it used throughout the history. The one I used was popular around Verdun in the Great War.
To make the circular parts stick better I entangled them strongly around the lower straight wire.
The supports are made of plastic sprue parts fixed with pins from below.
For 6" of fencing you need around 100cm of wire and three sticks.