Corrugated plastic signs work great for me too, except I source mine from Ag field signs. Guys pull them out in September before harvest and they just get tossed in the trash - so I used to drive around and pick them up for a lot of guys. Some of them have two piece stakes as well, a steel spike with an extruded plastic shank - these are great for making IDPA/IPSC targets (I have a couple cardboard templates and a big paper cutter to speed up shaping) - a guy can strike the edges, meaning strike the stake, and not worry about ricochets. Now I'm working for an Ag seed & chemical company, so I have access to the signage all year long, at no cost.