Length of Animation from Animator

I have an animation which plays once, and it played once just fine. I want to Invoke a method as soon as the animation finishes. I have been researching and experimenting for over an hour now, but without the result I want. I try to get the animation from the Animator, but Unity says my animation is not attached. The thing is, I don't care if it's attached...I just want to know how long it is, not actually do anything with it. How can I achieve this? Here is the code which results in the error:

CODE:

 using UnityEngine;
 using System.Collections;
 
 [RequireComponent(typeof(PolygonCollider2D))]
 [RequireComponent(typeof(Animator))]
 public class Construction : MonoBehaviour
 {
     // Use this for initialization
     void Start()
     {
         Invoke("EnableObstacleState", GetComponent<Animator>().animation.clip.length);
     }
 
     private void EnableObstacleState()
     {
         GetComponent<PolygonCollider2D>().enabled = true;
     }
 }

ERROR:

 MissingComponentException: There is no 'Animation' attached to the "Barricade(Clone)" game object, but a script is trying to access it.
 You probably need to add a Animation to the game object "Barricade(Clone)". Or your script needs to check if the component is attached before using it.
 Construction.Start () (at Assets/Scripts/Construction.cs:11)