The Answer is "Don't Fence Me In".
The question is "What are these men singing?"
Concertina Wire was not yet an item of supply. Barbed wire had been invented in the USA and patented by Joseph Glidden in 1874. It was used to construct protective fences by US troops in the Spanish American War. By the 1900s the military use of barbed wire was common. Each side used different patterns for their fences, the US Army manual described over six different ways to employ barbed wire. Foot traps (tanglefoot), vertical fences, single and double apron fences, single and multiple rounds, the list goes on. In each case single strands of wire were stretched from support to support and attached or tied off. In all cases a principal ingredient was muscle power and sweat.
In this picture Engineers supervise, and take the credit, while the hammer and nail work is done by, you guessed it, line troopers. Notice the round hoops or spacers being installed between the strands of wire. When the fence is complete the wooden beams will be removed to preclude their use as crossing aids.
As time passed the use of wire continued but not in the formal manner once seen. German razor tape and concertina wire replaced strands of barbwire. In Vietnam it was used to slow or channel enemy attacks and was placed out in loose rolls, one, two or three layers high. These stacks were not fences, rather they were obstacles and covered with preplanned direct fire. When the unit moved the wire was taken up and moved with the unit to be used again.