Yeah, I know it's always an arms race, but the trick is to always give them something they weren't anticipating that's hard to deal with in code. There are always methods that would alert a human to something odd going on that don't alert the bot's methods for perceiving its surroundings.

One of the best tricks is to show them messages via a method outside of normal chat which a normal player would see on their screen, but which a bot would not receive as 'chat'.