GUI 3D draw in terrain

Hello, I am thinking about how to make a gui in terrain, or represent image in terrain when you use skill to know the direction of skill graphically. I tryed GUI.DrawTexture() but it takes a rectangle wich has x and y but not z, there is any method to do it? Really is difficult to explain so I put an image, for those who played lol I mean this (in red):

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Thanks for answers, in my C# code I wrote this:

plane = GameObject.CreatePrimitive(PrimitiveType.Plane);

And after that I could create a shader to the plane and rotate it to mouse position. Thanks.

You can use Projector component to achieve this, especially in view of uneven ground.