• A thief stands on a road. When the road is completed and they can no longer earn any more points they return.
• A knight stands in a city. When the city is completed and they can no longer earn any more points they return.
• A monk stands in a monastary. When all the surrounding tiles have been placed and they can no longer earn any more points they return.
• A farmer lies in a field. When the field is closed off and all the cities on that field have been completed so they can no longer earn any more points, they continue lying in the field, useless until the end of the game.

I would like to change that last one. If a farmer has earned all the points they can because their field is closed off and all the cities on it are completed [1], they should return with points just like everyone else.

[1] This assumes you are using the most recent city scoring rules of three points per completed city calculated on a per farm basis. This is different from the original rules of four points per completed city calculated per city.