Using NGUI, how do I add a circle under a model's feet like World of Warcraft?

So I’ve been trying to figure out how to add a circle under an NPC’s feet like it’s done in WoW. I’m using NGUI, but I don’t know if this is something that’s done using a GUI element or with some sort of texture. I’ve looked it up, but to be honest, I don’t know what it’s called so that’s making it difficult.

Also, in WoW the circle adjusts to terrain, so it doesn’t clip through. Is there something special needed to do that?

Any help would be greatly appreciated.

You wouldn’t use NGui for this. use a projector instead.