Answer by MrSoad

Using a plane as a collider is maybe not the best idea, it can be quite easy to pass through a mesh collider attatched to a plane. You are better off using a box collider with some depth to it. For adding posters, paths etc look at the available Decal Systems on the asset store, they do exactly what you need and will avoid the Z fighting issues that you will probably get from doing it Cherno's way.