GUILabel to GUIText or Textmesh

Hi everyone, I'm having a little problem with my script:

 #pragma strict
 var targetScreenPosition : Vector3;
 var Mname = "MonsterName";
 
 function Start () {
 
 }
 
 function Update () {
 
 }
 
 function OnGUI(){
     targetScreenPosition = Camera.main.WorldToScreenPoint(transform.position);
     targetScreenPosition.y = Screen.height - targetScreenPosition.y;
     targetScreenPosition.x = targetScreenPosition.x - 20;
     if(targetScreenPosition.z > 0){
     GUI.Label (new Rect (targetScreenPosition.x,targetScreenPosition.y,100,50),Mname);
     }
 }

What I'm trying to do here is an script that shows name of monster to the player always right (it turns where player goes) but the problem with this is I can't hide GUILabel's if they're behind the wall. So I would need to transform this script so it works with GUIText or Textmesh so I could hide that text if player doesnt see that current gameobject, but I dont really have no idea how to get it work with textmeshes or guitext so that those would load Mname variable as their texts.

I'm sorry if this has been an bad explanation.