Making objects visible when nothings collide with it

I use these codes to make "ArrowObj" become visible when another game object collide with "HelpStartBox", it works:

 public var ArrowObj:GameObject;
  
 function Start () {
     ArrowObj.renderer.enabled = false;  
 }
 
 function OnTriggerEnter(col:Collider) {
 
     if(col.gameObject.name=="HelpStartBox"){
         ArrowObj.renderer.enabled = true;
         yield WaitForSeconds(2);
         Application.LoadLevel (1);
         Debug.Log("1");
         }
 }

But when I want to make "ArrowObj" become invisible when nothings collide with "HelpStartBox", I don't know what to do. I have tried to put these codes but it didn't work.

 else {
     ArrowObj.renderer.enabled = false;
 }

What should I do?