RewriteEngine on

RewriteCond %{REQUEST_URI} !/admin/*
RewriteCond %{REQUEST_URI} !/redirect*
RewriteCond %{REQUEST_URI} !/include/*

RewriteRule ^gary/test_directory/([A-Za-z]+)/[A-Za-z]+/?$ /gary/test_directory/subcategory.php
RewriteRule ^gary/test_directory/([A-Za-z]+)/?$           /gary/test_directory/maincategory.php