So I thought I'd make use of the things I have lying around the house then I dont have to wait for it to arrive and I could get on with my prop that same evening
It's a very simple and easy technique that I hope people will follow and use in the future.
Step 1: The Materials
String, roughly 2.5 times more string than you want barbed wire.
PVA glue, the staple of many a project
Grey Paint, I used grey poster paint, actually white and black mixed but anything that will mix with the glue will be fine.
Make up a pot of glue. I diluted mine down 1:1 with water, which means it dries softer and is easier to work with. I mixed the grey paint into the glue at this stage to ensure nice even colouring. Roughly 4:1 is my ratio of dilluted glue to paint.