For pieces of rebar, I would use something like a small length cut from a paper clip. Exact scale would not be too important because you wouldn't know exactly what size of rebar they used originally in the construction.
As for the VLS barbed wire, I have used it a couple of times in the past and am happy with the results. The barbed wire in the following pic is the verlinden product.
Happy Modelling and God Bless
Robert