better_wordpress_transient_cache.php

<?php
// Function to regenerate the data and save the transients
function special_query(){
  $special_query_results = new WP_Query( 'cat=5&order=random&tag=tech&post_meta_key=thumbnail' );
  set_transient( 'special_query_results' , $special_query_results, 12 * HOUR_IN_SECONDS );
  set_transient( 'special_query_results_no_expire' , $special_query_results, 99 * YEAR_IN_SECONDS );
  return $special_query_results;
}

// Get any existing copy of our transient data
if( false === ( $special_query_results = get_transient( 'special_query_results' ) ) ){
  // It wasn't there, so let's use the cache that doesn't expire
  if( false === ( $special_query_results = get_transient( 'special_query_results_no_expire' ) ) ){
    // If for some reason our forever cache is missing, run the query
    $special_query_results = special_query();
  } else {
    // Our forever cache exists, but we need to update the data and save the transient on shutdown
    add_action('shutdown', 'special_query');
  }
}
// Use the data like you would have normally...

It works if you don't need to receive any variables for special_query() to return some data. If special_query were to receive an argument...zing!