I have a couple of suggestions in order to implement fast, efficient and also non-intrusive anti-bot solutions.
1. Adding Additional Novice Grounds Dialogues
This one is very simple, the Grampa NPC that gives you the little exam on scamming can be changed to add one question where you have to fill-in.
The script is very simple, you make it so that "CorrectAnswer=CharacterName" that way human players can just fill in their names, whereas automated bots will be temporary disabled and will be stuck at the 1st map of the novice grounds.
This permits you to efficiently filter out the ZennySpammers for a while since they will not be able to recreate a novie and warp to Prontera.
P.S: Its funny as hell that they are using name generators to bypass the gribberish filter
2. Editing Some of the Map's GRFs
Including custom training grounds maps and towns such as an exact replica but with a different .grf will definitely disable all bots until they can dissassemble the .grf and start to realize that the .grf files were tampered with. This will essentially disable all low-entry/beginner level botters and will put pressure and work on intermediate botters to pull their resources together to re-enable mass botting.
3. Having a Right-click Report Player Button (Come'on its one line of script)
Do you know that we could simply have a right-click report player button, that way you could enable a lot of the server's human population that doesn't register on the forums to participate in reporting. Moreover you should be aware that botters constantly monitor the BOT REPORT THREAD to cover themselves. So having an in-game reporting system would essentially prevent them from spying upon reports and thus meddling with the GM Affairs.
Lastly, these solutions are easily implementable and doesn't require an anti-bot shield.. (Money Saved?)