mouse click obj to initiate action, then locking the obj so action cant be repeated

when i click on the target object it starts its partical animation and registers that one target has been activated, the issue im having is that the player can hit the same target over and over and it will register that multiple targets have been hit, how do i fix my script to show that one target has been hit and that the hit target can no longer be affected by the player once activated?

here is the obj partical animation script

 var fire: GameObject;
 var smoke: GameObject;

function OnMouseDown(){

 var campSound: AudioSource = GetComponent(AudioSource);
 campSound.Play();
 
 var flame: GameObject = Instantiate(fire,transform.position, Quaternion.identity); 
 var flameEmitter: ParticleEmitter = flame.GetComponent(ParticleEmitter);
 flameEmitter.emit=true;
 
 var smoke: GameObject =   Instantiate(smoke,transform.position, Quaternion.identity); 
 var smokeEmitter: ParticleEmitter = smoke.GetComponent(ParticleEmitter);
 smokeEmitter.emit=true;
 
 GameObject.Find("Clock").GetComponent("Clock script").remainedTarget-=1;

and this is the timer script, once the time is up the player is taken to the winning or losing pages(that part works my issue is making it so the player CANT hit the same target over and over in order to win)im not sure if this part of my script needs editing but to be safe ill include it.

function TimeIsUp(){

 lives = (PlayerPrefs.GetInt("Player Lives")) - 1;    //*** Get the value of “Player lives” and -1
 PlayerPrefs.SetInt("Player Lives", lives );    // *** and assign it to the local lives variable.
 if (remainedTarget == 0) { Application.LoadLevel(3);}                // *** Winning Condition
 else if (lives == 0) { Application.LoadLevel(4); }            // *** Losing Condition
 else {
     Application.LoadLevel(1);    // *** Reload the current Scene
 }

}