SVN 9977 Exploit: abuse pillaging of mines you built yourself
Find a hill outside of everybody's territory.
Place a stack of workers and a military unit there.
Build a mine (which is allowed outside of your borders, same for roads and quarries)
Pillage the mine with your military unit
Repeat
for a substantial amount of money each time you pillage. It is offset by unit upkeep, but if you don't have anything else to do with your workers, and you don't want to delete them, this way they give you additional money.
Recommended: don't allow pillage of neutral territory. Also the amount of money you get from pillage in enemy territory is quite high. 130 gold for an enemy mine!? these only produce 2-3 hammers/turn if I remember correctly. Where is the money coming from?