Missile Behavior improvement

I have a missile that follow the nearest target with a specific tag. ok so now… its perfect.
But i want that: when a missile pass the target (relative to player) the missile do not follow anymore… just translate forward.

something like this pseudocode:

distance of missile relative to player;
distance of target relative to player;

when the distance of missile > distance of target
just go forward;

and this is my actual code:

using UnityEngine;
using System.Collections;

public class Missle : MonoBehaviour {
	
	public string searchTag;
	private GameObject closetMissle;
	private Transform target;
	public GameObject missileExpObject;
	
	void Start()
	{
		closetMissle = FindClosestEnemy();
		
		if(closetMissle)
			target = closetMissle.transform;
	}   
	
	void Update()
	{   

		transform.LookAt(target);
		transform.Translate(Vector3.forward * 30f * Time.deltaTime);

		if(target == null)
		{
			closetMissle = FindClosestEnemy();
			
			if(closetMissle)
			{
				target = closetMissle.transform;
			}
		}
		Destroy (this.gameObject,12);
	}
	
	GameObject FindClosestEnemy()
	{
		GameObject[] gos;
		gos = GameObject.FindGameObjectsWithTag(searchTag);
		
		GameObject closest = null;
		float distance = Mathf.Infinity;
		
		Vector3 position = transform.position;
		
		foreach(GameObject go in gos)
		{
			Vector3 diff = go.transform.position - position;
			float curDistance = diff.sqrMagnitude;
			
			if(curDistance < distance)
			{
				closest = go;
				distance = curDistance;
			}
		}
		
		return closest;
	}
}

where i put this implementation? and how
regards…

You can use a sphere cast that casts forward once every second/x amount of frames and when it doesn’t have a hit of the player anymore, stop casting and stop looking at target. Which means transform.LookAt() will need too be in an if(bool) statement, and the spherecast will if it gets a hit will set bool to true, and if not it will set bool to false. That’s the best way I could think of. Sphere casting might use a lot of math though. So you might want to check by angle between the target and the missile forward.