Simply in order to zone out of a town into an area have the party lead be required to enter a random three or four digit code. Show the party leader the code, he/she enters and clicks OK, off you go.
I don't know how much coding effort that would be and until you got used to it it would feel like an inconvenience, but bot programs would become effectively extinct, or at worst every bot farmer would have to monitor each bot 24/7 to enter the codes for farming.
It would work.
I would still like to see bot traps in town though... fences that appear in the bots paths and herd them like cattle.
