How can i avoid the enemy to sight me through walls?

Hi there! I managed myself to find some resources around the internet and at the end this script came out! :3 Sadly, now i have the problem that i do not know how to avoid the enemy "Detecting" the player trough, for example a cube or a wall. Any ideas? =)

... Also, if for whatever reason the user getyour411 happens to be reading this i'll be glad for you to know that i never asked for a Script!! ¬¬ If so, i wouldn't bothered mattyman174 to explain me "HOW" not give me a way of avoid detection through walls.

 using UnityEngine;
 using System.Collections;
 
 public class EnemyAI : MonoBehaviour {
     public Transform player;
     float distancefrom_player;
     public float look_range = 20.0f;
     public float agro_range= 10.0f;
     public float move_speed= 5.0f;
     public float damping = 6.0f;
     // Use this for initialization
     void Start () {
         
     }
     
     // Update is called once per frame
     void Update () 
     {
         distancefrom_player = Vector3.Distance (player.position, transform.position);
     }
     void FixedUpdate()
     {
         if (distancefrom_player < look_range ) 
         {
             transform.LookAt(player);
         }
         
         if (distancefrom_player < agro_range) 
             
         {
             attack();
         }
     }
     
     void lookAt()
     {
         Quaternion rotation = Quaternion.LookRotation (player.position - transform.position);
         transform.rotation = Quaternion.Slerp (transform.rotation, rotation, Time.deltaTime * damping);
     }
     
     void attack()
     {
         transform.Translate (Vector3.forward * move_speed * Time.deltaTime);
     }
 }