using UnityEngine;
using System.Collections;

public class Generate : MonoBehaviour {

     public GameObject rock;
     public int score = 0;
         
     void Start ()     
     {
      InvokeRepeating("CreateRock", 1f, 1.5f);
     }
         
     void OnGUI()
     {
      GUI.color = Color.black;
      GUILayout.Label(" Score: " +score.ToString());
     }

     void CreateRock ()     
     {
      Instantiate(rock);
      Destroy(rock, 5); //Эту строчку я добавил
      score++;
     }
}

void OnCollisionEnter(Collision *объект*)