how to Stop Enemys from clipping into eachother?

I have a 3d zombie arcade game, I want it to be more of a horde insted of one glitchy zombie with 300000 arms (get it their all clipped into eachother? because of the fallowing you nav thing). Heres my scrips for all my zombies, i really need help thanks!

 using UnityEngine;
 using System.Collections;
 using UnityEngine.AI;
 
 public class EnemyController : MonoBehaviour {
     NavMeshAgent nav;
     Transform player;
     Animator Controller;
 
     // Use this for initialization
     void Awake () {
         nav = GetComponent <NavMeshAgent> ();
         player = GameObject.FindGameObjectWithTag ("Player").transform;
         Controller = GetComponentInParent<Animator> ();
     }
 
     // Update is called once per frame
     void Update () {
         nav.SetDestination (player.position);
         Controller.SetFloat ("speed", Mathf.Abs (nav.velocity.x + nav.velocity.z));
     }
 }