Sphere Collider with Terrain

I am trying to get my gameobject to move 180 degrees if it walking into a wall, or a tree (any terrain). I am using the onTriggerStay function, but it is not registering.

Here is the code snippet for the detection.

void OnTriggerStay (Collider hit) { if (hit.tag == "Terrain") { Debug.Log ("Not Touching"); wallhit = true; } else { wallhit = false; } }

For some reason it is not triggering when the game object does walk into the wall. Any help please?!

I have made sure that the istrigger is checked for the sphere collider, and I have made sure that the tag for the terrain is called "Terrain".