Only instantiate random seed once

Hello world,

I have a code spawning me some blocks in a grid:

 var gridX = 16;
 var gridY = 16;
 var spacing = 10.0;
 var xPosition = 0.0;
 var yPosition = 0.0;
 var blocks : GameObject[];
  
 function Start () {
  for (var y = 0; y < gridY; y++){
  for (var x = 0; x < gridX; x++){
  Instantiate(blocks[Random.Range(0, blocks.Length)], Vector3 (x+xPosition, y+yPosition, 0) * spacing, Quaternion.identity);
  }
  }
 }

I assign the blocks in the Inspector and would like to restrict it from picking a certain prefab more than once. Is it possible to tell the instantiation to do that?

Cheers