A quick catch-all cache-busting WordPress plugin when having clients clear their browser cache isn't an option.

nocache.php

<?
/**
 * Plugin Name:   WordPress Catch All Cache Buster
 * Description:   A quick catch-all cache-busting WordPress plugin when having clients clear their browser cache isn't an option.
 * Version:       1.0.0
 * Author:        Joseph Roberts
 * Author URI:    https://github.com/DigitalJoeCo
 * License:       MIT
 * License URI:   http://opensource.org/licenses/MIT
 */

defined( 'ABSPATH' ) or exit; // Exit if accessed directly.

add_action('template_redirect', function() {
    if(!isset($_COOKIE['nocache']) and !$_GET['nocache']){
        $location = esc_url(add_query_arg('nocache', (string) rand(00000, 99999)));
        wp_redirect($location);
    }
});