how to display object while ! raycast hit is true ?

hey at all, i need some help (once more)

i want a plane with a crosshair texture to be displayed when the enemy object is hitten by a raycast from the player ( if foundhit = true) it basically works but not continiously while its being hitten. it's displayed for a short moment, then it disappears, then it is displayed again for a short moment (and so on) while the ray hits the enemy. seems it's because of the update funct. certainly i tried to set it to : while(foundhit = true) and certainly unity stucked.
how to achiefe that it is displayed while! the ray hits ?
thx previously

here's the code:
using UnityEngine; using System.Collections;

 public class Crosshair : MonoBehaviour {
     public Transform raytrf;
     public float raycastDist = 1000.0f;
     public string tagCheck = "Enemy";
     public bool foundHit;
     public bool checkAllTags = true;
     RaycastHit crosshair_hit;
     //private Renderer rend;
     public GameObject thisplane;
 
     // Use this for initialization
     void Start () 
     {
         //rend = GetComponent<Renderer> ();
         //rend.enabled = false;
     }
     
     // Update is called once per frame
     void Update () 
     {
         //bool foundHit = false;
         RaycastHit crosshair_hit = new RaycastHit();
         foundHit = Physics.Raycast(transform.position, transform.forward, out crosshair_hit, raycastDist);
         //Vector3 forward = raytrf.TransformDirection(Vector3.forward.normalized) * 1000;
         //Debug.DrawRay(raytrf.position,forward, Color.red);
 
         if (foundHit && checkAllTags && crosshair_hit.transform.tag != tagCheck)
         {
             foundHit = false;
             //rend.enabled = false;
         }
         if (!foundHit) 
         {
             thisplane.layer = LayerMask.NameToLayer ("Invisible");
             //rend.enabled = false;
             //Debug.Log("false");
         } 
         else 
         {
             if(foundHit) 
             {
                 thisplane.layer = LayerMask.NameToLayer ("Default");
                 //rend.enabled = true;
                 //Debug.Log("hit");
             }
         }
 
     }
 
 }