Pick up and carry objects [Problem]

I have one problem with my pick up and carry objects script. The problem is, the objects can go through the walls (other objects). Is there any way to fix this problem? Thank you!

The script:

Code (JavaScript):

1. var onhand : Transform;
2. public var Distance : float;
3. public var pickUp_Distance : float;
4. var player : Transform;
5.  
6. function Update ()
7. {
8.  
9. }
10.  
11. function OnMouseDown ()
12. {
13.     Distance = Vector3.Distance(player.position, this.transform.position);
14.     if(Distance <= pickUp_Distance)
15.     {
16.         GetComponent.<Rigidbody>().useGravity = false;
17.         GetComponent.<Rigidbody>().constraints = RigidbodyConstraints.FreezePositionX | RigidbodyConstraints.FreezePositionZ | RigidbodyConstraints.FreezePositionY;
18.         this.transform.position = onhand.position;
19.         this.transform.rotation = Quaternion.identity;
20.         this.transform.parent = GameObject.Find("Player").transform;
21.         this.transform.parent = GameObject.Find("Main Camera").transform;
22.     }
23. }
24.  
25. function OnMouseUp ()
26. {
27.     this.transform.parent = null;
28.     GetComponent.<Rigidbody>().constraints = RigidbodyConstraints.None;
29.     GetComponent.<Rigidbody>().useGravity = true;
30.  
31. }