Just built several barbed wire obstacles (Spanish Rider or Knife Rests or something like that . . . ). Used Battlefield Accessories barbed wire and bass wood sticks. Base is plastic sheet with Durham Rock Hard putty mixed with suitably sized gravel. Wood structure stuck into putty and when it dries it holds the "X" shaped rests. I wrapped the barbed wire around the lateral beam and glued the beam down. Painted wire with black gesso and then a rusty shade of brown.
Hay stacks were my other creation. I'm working with some faux fur for fields (say that real fast several times) and what I shave off the fur can be pressed into a ball, sprayed with varnish, stuck to cardboard and shaped some as the varnish dries. Cover the cardboard base with your choice of basing materials. One other tip, I dry brush the fur with a highlighting paint to not only highlight the fur field but also to make it easier to shave or trim. Otherwise you have the fur sticking everywhere. Painted, it tends to clump together when cut and that is where I got the idea of making hay stacks.