How to lock the Z axis so my Enemy just flips on the Y axis

Hi there,

So I have the script below and i need my enemy to follow the player (which it is doing).

Then when the player starts moving the opposite way I need the enemy to just flip on the Y axis so the sprite is facing the correct way.

What I don't want the enemy to do is to rotate on the Z axis as if the enemy is following the player as it jumps and falling backwards.

I want to lock the enemy's Z axis if you understand what I mean.

Thank you! :)

---The Code---

Using UnityEngine; Using System.Collections;

 public void Awake()
 {

     myTransform = transform;
 }
 public void Start()
 {

 }

 public void Update()
 {
     transform.LookAt(Player.position);

     transform.Rotate (new Vector3 (0, -90, 0));//correcting the original rotation

     //move towards the player
     if (Vector3.Distance(transform.position,Player.position) > MinDistance)
     {    
         //move if distance from target is greater than 1
         transform.Translate(new Vector3(MoveSpeed* Time.deltaTime,0,0));
     }

     if(Vector3.Distance(transform.position,Player.position) <= MaxDistance)
     {

     }
 }