Name: SPECIFIC CHARACTERS
Version: 1.1
Description: Denies any request for a url containing characters other than "a-zA-Z0-9.+/-?=&" - REALLY helps but may break your site depending on your links.
Rules: 
RewriteCond %{REQUEST_URI} !^%relative_root%(wp-login.php|wp-admin/|wp-content/plugins/|wp-includes/).* [NC]
RewriteCond %{THE_REQUEST} !^[A-Z]{3,9}\ [A-Z0-9\.\+_/\-\?\=\&\%\#]+\ HTTP/ [NC]
RewriteRule .* - [F,NS,L]