how to make triger fireball not to pass through spesific objects

hey guys I am a begginer user of unity3d and i would like to learn how i can make fireballs which are shooted by my turrets (and are trigger) not to pass through spesific walls or grounds i have put.. so here is my scripts

Movement Script:

 //Moving Around
 var speed = 3.0;
 var rotateSpeed = 3.0;
 var mouserotationSpeed : float = 5.0;
 //Shooting
 var bullitPrefab:Transform;
 //Dying
 static var dead = false;
 //Getting Hit
 var tumbleSpeed = 800;
 var decreaseTime =.01;
 var decayTime = 0.01;
 static var gotHit = false;
 private var backup = [tumbleSpeed, decreaseTime, decayTime];
 //Jump
 var jumpSpeed : float = 8.0;
 var gravity : float = 5.0;
 
 function LateUpdate()
 {
 if(dead)
 {
 transform.position = Vector3(0,20,0);
 gameObject.Find("Main Camera").transform.position = Vector3(0,4,-10);
 dead = false;
 }
  
 if(gotHit)
 {
 if(tumbleSpeed < 1)
 {
 //we're not hit anymore... reset & get back in the game!
 tumbleSpeed = backup[0];
 decreaseTime = backup[1];
 decayTime = backup[2];
 gotHit = false;
  
 }
 else
 {
 //we're hit! Spin our character around
 transform.Rotate(0,tumbleSpeed * Time.deltaTime,0, Space.World);
 tumbleSpeed = tumbleSpeed - decreaseTime;
 decreaseTime += decayTime;
 }
 }
 }
 
 //function OnControllerColliderHit(hit:ControllerColliderHit)
 function OnTriggerEnter(hit : Collider)
 {
 if(hit.gameObject.tag == "fallout")
 {
 dead = true;
 HealthControl.LIVES -= 1;
 }
  
 if(hit.gameObject.tag == "enemyProjectile")
 {
 gotHit = true;
 HealthControl.HITS += 1;
 Destroy(hit.gameObject);
 }
 }
 
 function Update ()
 {
 var controller : CharacterController = GetComponent(CharacterController);
     if (controller.isGrounded) 
     {
         // We are grounded, so recalculate
         // move direction directly from axes
         moveDirection = Vector3(Input.GetAxis("Horizontal"), 0,
                                 Input.GetAxis("Vertical"));
         moveDirection = transform.TransformDirection(moveDirection);
         moveDirection *= speed;
         transform.Rotate(Vector3(0, Input.GetAxis("Mouse X"), 0) * Time.deltaTime * mouserotationSpeed);
         
         if(Input.GetButton("Jump")) 
         {
             moveDirection.y = jumpSpeed;
         }
     }
 
     // Apply gravity
     moveDirection.y -= gravity * Time.deltaTime;
     
     // Move the controller
     controller.Move(moveDirection * Time.deltaTime);
 
 //shoting
 if(Input.GetButtonDown("Fire1"))
 {
 var bullit = Instantiate(bullitPrefab, transform.Find("Spawn").transform.position, Quaternion.identity);
 bullit.tag = "wormProjectile";
 bullit.rigidbody.AddForce(transform.forward * 3000);
 }
  
  if(transform.position.y < -200)
 {
 dead = true;
 HealthControl.LIVES -= 1;
 }
 }

  @script RequireComponent(CharacterController)

Turret Script:

 var distanceTillShoot : float;
 var LookAtTarget : Transform;
 var damp : float = 6.0;
 var bulletPrefab : GameObject;
 var savedTime = 0;
  
 function Update ()
 {
 if(LookAtTarget)
 {
 var rotate = Quaternion.LookRotation(LookAtTarget.position - transform.position);
 transform.rotation = Quaternion.Slerp(transform.rotation, rotate, Time.deltaTime * damp);
 var seconds : int = Time.time;
 var oddeven = (seconds % 2);
 if(oddeven)
 Shoot(seconds);
 transform.LookAt(LookAtTarget);
 }
 }
 
 function Shoot(seconds)
 {
     if(seconds!=savedTime)
     {
         var bullet = Instantiate
 
 (bulletPrefab, transform.Find
 
 ("spawnPoint").transform.position, 
 
 Quaternion.identity);
         bullet.gameObject.tag = 
 
 "enemyProjectile";
         bullet.rigidbody.AddForce
 
 (transform.forward * 2500);
         
         savedTime=seconds;
     }
 }