Draw GUI behind some 3D-Object

Hello all !

I'm in trouble with a GUITexture. ='(

I want to show off my GUITexture next to a Interactive 3D Object, when I trigger it...
I use this Script to move my GUITexture next to my 3D Object :

Code (csharp):

1. using UnityEngine;
2. using System.Collections;
3.  
4. public class Btn_Action : MonoBehaviour {
5.  
6.     public Transform target;
7.     private Vector3 wantedPosition;
8.     private Vector3 positionReal;
9.  
10.     // Use this for initialization
11.     void Start () {
12.    
13.     }
14.    
15.     // Update is called once per frame
16.     void Update () {
17.         positionReal = new Vector3(target.position.x,target.position.y+0.5f,target.position.z);
18.         wantedPosition = Camera.main.WorldToViewportPoint(positionReal);
19.         transform.position = wantedPosition;
20.     }
21. }

My problem is that the GUITexture is in front of all my 3D Object... I tried with this Tuto :
unity3d-creating-a-gui-with-both-3d-and-2d-elements

But it's didn't work... (I modified my Script for use the Second Camera) - GUITexture who don't follow my Target, everytime in front of my 3D-Objects...

Code (csharp):

1. using UnityEngine;
2. using System.Collections;
3.  
4. public class Btn_Action : MonoBehaviour {
5.  
6.     public Transform target;
7.     private Camera camera;
8.     private Vector3 wantedPosition;
9.     private Vector3 positionReal;
10.  
11.     // Use this for initialization
12.     void Start () {
13.    
14.     }
15.    
16.     // Update is called once per frame
17.     void Update () {
18.         if(camera == null)
19.         {
20.             camera = GameObject.FindWithTag("CameraBtn").camera;
21.         }
22.         positionReal = new Vector3(target.position.x,target.position.y+0.5f,target.position.z);
23.         wantedPosition = camera.WorldToViewportPoint(positionReal);
24.         transform.position = wantedPosition;
25.     }
26. }

Need Help !! Thanks =)