How to make a cube (go to a certain position) after colliding with a plane?

[LesWizard]

i recently got unity 3D and i have started making a game consisting of 2 cubes trying to knock each other off the arena. i am having some trouble with making the cube detect collision with the plane underneath the arena which i want it to make the cube re spawn when ever it touches it.
i have done this so far:

using UnityEngine;
using System.Collections;

public class plz : MonoBehaviour
    {
        void OnCollisionEnter(Collision col)
        {
            if (col.gameObject.name == "Death")
            {
                transform.localposition = new Vector3 (10.56507f, -13.15086f, 9.080673f);
            }
        }
    }

PLEASE HELP!!

[bubzy]

edited the answer to format the code correctly, in future use the “101010” button, it makes it easier to read

why not just check the current height of the cube?

public Vector3 spawnPos = new Vector3(10,1,9);
public float deathHeight = -13f;
public int lives = 3; 
//these are all public so that you can change them in the editor

void Update()
{
if(transform.position.y < deathHeight)
{
lives --; //lose a life
transform.position = spawnPos; //move the object back to the spawn position
}

hope this helps in some way