What about a quota on the number of rocks people can mine a day? That way, if people macro they could only get a certain amount everyday. Alternatively, for those who have been caught macroing before, they could be charged a nominal fee of 250 gralats to enter the mine so as to discourage them from mining. They would also be charged a utility fee of 50 gralats everytime they use the machine in the mines, so as to offset the amount of money they earn from macroing.