Trying to get score counter...

I got my score counter to show up on my GUI Text, yet when I switch to another object with the same script its resets the score to zero. What can i change or add to stop it from resetting?

 var speed = 5;
 var buck = 100;
 var deer = 10;
 private var score : int = 0;
 var ScoreBoard: GUIText;
 
 
 function Update () {
     transform.position += Vector3.forward * Time.deltaTime * speed;
 }
 
 function OnMouseEnter () {
     Debug.Log("Hit");
     speed = 15;
     deer += 10;
     ScoreBoard.text = ("Score: ") + deer;
 }    
 
 function OnMouseExit () {
     Debug.Log("Safe");
     speed = 5;
 }