Or if you can't (or don't know how to) move your files, you can do a tricky thing.
Something like if your cron file is omg.php, edit it to omg.php?sPass=secretcronpass
And then check if passwords match in your files, like:
<?
//this is omg.php
if($_GET['sPass']!='secretcronpass') exit('Type here anything or leave it ^_^');
?>