Set NOINDEX, NOFOLLOW on particular products

Question

My magento store has the following to allow google/search engines to crawl the entire site.

<meta name="robots" content="INDEX,FOLLOW" />

I am now in need for some particular products to have:

<meta name="robots" content="NOINDEX,NOFOLLOW" />

so that google doesn't crawl/index them. Is this possible? Products would be random (i.e not all from one category) so I need to be able to do this on a product by product basis if needed.

I know i could do it on a url basis like:

<?php
$currentUrl = Mage::helper('core/url')->getCurrentUrl();
if ($currentUrl == 'xxxxxxx')
{
    <meta name="robots" content="NOINDEX,NOFOLLOW" />
}
else
{
    <meta name="robots" content="INDEX,FOLLOW" />
}
?>

but there could end up over time to be hundreds/thousands of these.

Answer 1

In Magento admin, when editing a product go to the tab design and add the following to custom layout:

<reference name="head">
      <action method="setRobots"><meta>NOINDEX,NOFOLLOW</meta></action>
</reference>

Answer 2

you can observe the event controller_action_layout_generate_blocks_after like this:

public function setRobots($observer) 
{
     $controller = $observer->getAction();
     $fullActionName = $controller->getFullActionName();
     if ($fullActionName == 'catalog_product_view') { //if on product page
          $product = Mage::registry('product'); //access the current product if needed
          if (your condition here) { //condition to set the robots to noindex, nofollow
              $observer->getLayout()->getBlock('head')->setRobots('NOINDEX,NOFOLLOW');
          }
     }
}