Another fun one is sending a redirect to a gzip bomb or extremely large file (i.e. speedtest download file) for when certain non-existant URLs are requested, i.e. /wp-login.php on a non-wordpress site.
If it's a file that nothing on your site links to, and doesn't really "exist" how would google ever index it? Especially if you put in as a deny in robots.txt, which as far as I'm aware, Google honors.