What is your reasoning for not using Friendly URLs?
Enabling Friendly URLs will generate URLs that are easy to read and include words that describe the content of the webpage. This allows most search engines to easily crawl your forum, and also allows for specially formatted URLs.
Secondly, if you refuse certain words processing on your domain, you may also be blocking ligetiment links that contain those phrases, such as ones that are contained in discussion topics or user names.
Site logs are primarily meant for site admins to use as a tools for debugging and adjusting site issues, as well as for reporting site actions.
in this case, you may be better off with finding who the offender is thats attempting to bypass your forums naturally generated URLs, and blocking them by absolutele IP address if its frequent occurrence over a period of time
