fly movement

Hello,

This is my first time on unity and I have some probleme in this script ( the fly can't fly in all the area) #pragma strict

 var displacement:Vector3 = Vector3(5,2,5);
 var desplVel:float = 1;
 
 
 private var pos0:Vector3;
 
 private var iniRndX:float;
 private var iniRndY:float;
 private var iniRndZ:float;
 
 private var audioOn:boolean=false;
 
 private var audioSourceMax:int = 4;
 private var audioSourceCurr:int = 0;
 
 function Start () {
     iniRndX = Random.Range(Random.Range(0,200), 500);
     iniRndY = Random.Range(Random.Range(0,200), 500);
     iniRndZ = Random.Range(Random.Range(0,200), 500);
     
     desplVel *= Random.Range(0.5, 2);
     
     pos0 = transform.localPosition;
     transform.localEulerAngles.y = Random.Range(1,360);
 }
 
 function Update() {
     
     //// Delete this Lines if you haven't an Audio Source attached to the GameObject
     if (!audioOn){
         if (Random.value < 0.01) {
             if(CheckAudioSourcesMax()) {
                 GetComponent.<AudioSource>().Play();
                 audioOn= true;
             } else {
                 GetComponent.<AudioSource>().enabled = false;
                 audioOn = true;
             }
         }
     }    
     ////
 }
 
 function FixedUpdate () {
     UpdateDespl();
 }
 
 function UpdateDespl() {
 
     var x:float = (Mathf.PerlinNoise(Time.time*desplVel +iniRndX, iniRndX) -0.46525) *displacement.x;
     var y:float = (Mathf.PerlinNoise(iniRndY, iniRndY+ Time.time*desplVel) -0.46525) *displacement.y;
     var z:float = (Mathf.PerlinNoise(iniRndZ, iniRndZ+ Time.time*desplVel) -0.46525) *displacement.z;
     
     
     var despl:Vector3 = Vector3(x,y,z);
     var rot:Quaternion = Quaternion.LookRotation(despl, Vector3.up);
     rot.eulerAngles.x = 270;
     rot.eulerAngles.z = 0;
     rot.eulerAngles.y += 90;
     
     GetComponent.<Rigidbody>().AddForce(despl, ForceMode.Force);
     transform.rotation = Quaternion.Lerp(transform.rotation, rot, 0.09);
      
     if ((transform.localPosition-pos0).sqrMagnitude>displacement.sqrMagnitude) {
         GetComponent.<Rigidbody>().AddForce((pos0 -transform.localPosition)*2, ForceMode.Force);
     }    
 }
 
 function CheckAudioSourcesMax():boolean {
     var maxNum:int = 0;
     var flyScripts:FlyBehav[] = FindObjectsOfType(FlyBehav);
     for(var flyScript:FlyBehav in flyScripts) {
         maxNum = Mathf.Max( flyScript.IncreaseAudioSourcesCurr(), maxNum);
     }
     if(maxNum<=audioSourceMax)    return true;
     else return false;
 }
 
 function IncreaseAudioSourcesCurr():int {
     audioSourceCurr ++;
     return audioSourceCurr;
 }

and I would like to know how to add a limit border to stay on the screen( maxX, minX, maxY, MinY) and the fly can fly in all the area like in this code

 #pragma strict
  var maxX = 6.17;
  var minX = -6.06;
  var maxY = 3.08;
  var minY = -5.63;
  
  private var tChange: float = 0; // force new direction in the first Update
  private var randomX: float;
  private var randomY: float;
  var moveSpeed = 10;
 
 function Start () {
 
 }
 
 function Update () {
      // change to random direction at random intervals
      if (Time.time >= tChange){
          randomX = Random.Range(-2.0,2.0); // with float parameters, a random float
          randomY = Random.Range(-2.0,2.0); //  between -2.0 and 2.0 is returned
          // set a random interval between 0.5 and 1.5
          tChange = Time.time + Random.Range(0.5,1.5);
      }
 
 
      transform.Translate(Vector3(randomX,randomY,0) * moveSpeed * Time.deltaTime);
      // if object reached any border, revert the appropriate direction
      if (transform.position.x >= maxX || transform.position.x <= minX) {
         randomX = -randomX;
      }
      if (transform.position.y >= maxY || transform.position.y <= minY) {
         randomY = -randomY;
      }
      // make sure the position is inside the borders
      transform.position.x = Mathf.Clamp(transform.position.x, minX, maxX);
      transform.position.y = Mathf.Clamp(transform.position.y, minY, maxY);
 
 }

Can anyone help me please ?

Thank's