Stop Audio clip from playing

I am making a horrorgame and want a sound to play when im passing a trigger. The problem is that it wont keeps being triggered every time I enter the trigger. What i want is to enter the trigger, play the sound, and then it has to never play again. I tried many things like destroying the clip.. but I cant seem to make it work properly.

public class SoundScript : MonoBehaviour 
{    
    public AudioClip Snd_Sound;

    IEnumerator Wait(){
        yield return new WaitForSeconds(20000);
        }

    void OnTriggerEnter(Collider col)
    {               
            audio.enabled = true;
            audio.PlayOneShot(Snd_Sound, 1f);
            StartCoroutine(Wait());
            //??? 
    }   
}

Also it seems that my wait for second doesn't function.