Foreach loop not running multiple times

The foreach loop only runs once and does not update any of the variables inside past the first run through

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3.  
4. public class Closestlock : MonoBehaviour {
5.     //Holds all GameObjects in the scene with the tag of Targetable.
6.     GameObject [] targetable;
7.     //The closest GameObject
8.     public GameObject targeted;
9.     // Use this for initialization
10.     // Used to calculate which GameObject is closer.
11.     public float minDist;
12.     public float dist = 0;
13.     // how quickly you want to be able to look at the target.
14.     public float speed;
15.  
16.     void Start () {
17.         //Fills the array with GameObjects
18.         //uncomment this line if you do not need to check if new objects are being instantiated
19.         //targetable = GameObject.FindWithTag("Targetable");
20.     }
21.    
22.     // Update is called once per frame
23.     void Update () {
24.         //The on/off switch
25.         bool targeting = true;
26.         //Fills the array with GameObjects
27.         targetable = GameObject.FindGameObjectsWithTag ("Targetable");
28.  
29.         //Runs through each GameObject
30.         StartCoroutine (Locking ());
31.         if (targeting) {
32.             // lock on target
33.             Quaternion targetRotation = Quaternion.LookRotation (targeted.transform.position - transform.position);  
34.             // Smoothly rotate towards the target point.
35.             transform.rotation = Quaternion.Slerp (transform.rotation, targetRotation, speed * Time.deltaTime);
36.    
37.         }
38.     }
39.  
40.     //Locking
41.     IEnumerator Locking(){
42.             foreach (GameObject target in targetable) {
43.                 //Stores the shortest distance and sets "targeted" to the shortest distance.
44.                 dist = Vector3.Distance (transform.position, target.transform.position);
45.            
46.                 //checks to see which is closer
47.                 if (dist < minDist) {
48.                     minDist = dist;
49.                     targeted = target;
50.                
51.                 } else if (minDist == 0) {
52.                     targeted = target;
53.                     minDist = dist;
54.                 }
55.            
56.             }
57.         yield return null;
58.     }
59. }

 

Check if line 27 Return Null or 0

 

When the script first runs it looks at the first object in the scene but it won't change what it looks at if another object comes close to it and the only variables that are not updating properly is dist and minDist