Only instantiate random seed once

Hi again, thanks for the answer.

Right, so I tried that and it works! However, it now spawns as many prefabs as I have in my list to choose from. Even though my grid is only 2x2, It'll still spawn all 10 I have in my list. Any idea what's wrong?

 var gridX = 16;
 var gridY = 16;
 var spacing = 10.0;
 var xPosition = 0.0;
 var yPosition = 0.0;
 var blocks : GameObject[];
 
 
  function Start()
  {
      GenerateBlocks();
  }
 
  function GenerateBlocks()
  {
  //make a copy of the original one
  //since we will be removing them from the array when we create them
  var blocksCopy : GameObject[] = blocks;
 
  for (var i = 0; i < blocks.Length; i++){
  for (var y = 0; y < gridY; y++){
  for (var x = 0; x < gridX; x++){
 
  //pick a random index
  var blocksNum : int = Random.Range(0, blocksCopy.Length-1);
 
  yield WaitForSeconds(1);
  Instantiate(blocksCopy[blocksNum], Vector3 (x+xPosition, y+yPosition, 0) * spacing, Quaternion.identity);
 
 
  var blocksJS : Array = blocksCopy;
  blocksJS.RemoveAt(blocksNum);
  blocksCopy = blocksJS;
 
 }
  }
  }
 }