Stop music from playing accidentally

Right now I have this script on a collider so it plays spooky music when my FPS player walks into it. but the problem I'm having is lets say my player hears the spooky music begin to play and descides "Say I better go back and get that shotgun!" and they accidentally trigger the music collider again so the music cuts off and begins to play again. How can I make it so it won't do that? That it will continue to play right through even if the player backs into the collider again,

var spookyStoneCircle : AudioClip;

function OnTriggerEnter(col : Collider){
    if(col.gameObject.tag == "Player"){
    audio.clip = spookyStoneCircle;
    audio.Play();
    yield WaitForSeconds (audio.clip.length);
    Destroy(gameObject);
    }
}

You could either have a private variable that tracks when the trigger has been fired once, or (the way I would recommend) you could check if the audio is already playing.

function OnTriggerEnter(col : Collider)
{
   if( !audio.isPlaying  // it will only progress if the audio isn't playing
      && col.gameObject.tag == "Player")
   {
      audio.clip = spookyStoneCircle;
      audio.Play();
      yield WaitForSeconds (audio.clip.length);
      Destroy(gameObject);
   }
}