Add captchas to slow down bots (e.g. whenever PBT finishes)
To help reduce botting why not add mandatory captchas at regular intervals if playing time exceeds a particular threshold (or simply whenever the village guard expires or the PBT finishes)?
Most bots are undoubtedly already capable of handling the PBT's without much "service interruption" beyond what is mandatory, so a captcha to get back into the game should pose a bit of a challenge for them :) Sure, captchas could be circumvented with sufficiently smart bots or low wage third world labour but considering the large number of different bots out there it's bound to slow down the vast majority.