RaycastHit behind object

Sorry only time for a very quick comment.

This can be done using LayerMask.

http://docs.unity3d.com/Documentation/Components/Layers.html

In the Inspector, click the dropdown box next to the variable myLayerMask. Tick to select the layers in which you want the raycast to work. Your colliders need to have their layers set to whatever you want. If you have everything on the same layer this will notwork.

 // JavaScript example.
 
 var myLayerMask : LayerMask;
 
 function Update() 
 {
     var hit : RaycastHit;
 
     // Does the ray intersect any objects excluding the myLayerMask layer
     if ( Physics.Raycast( transform.position, transform.forward, hit, Mathf.Infinity, myLayerMask ) ) 
     {
         Debug.DrawRay( transform.position, transform.forward * hit.distance, Color.yellow );
         Debug.Log( "Did Hit " + hit.collider.gameObject.name );
     }
     else 
     {
         Debug.DrawRay (transform.position, transform.TransformDirection (Vector3.forward) *1000, Color.white);
         Debug.Log( "Did not Hit" );
     }
 }