Precious Stones would lose their abilities after a pre-configured amount of time. Like a Godstone lasting for 15 minutes. Or City Protection for 1 hour. Precious stones could either disappear when time was up or lose their charge and could not be charged again. I would be willing to donate if this could be implemented.

Already added a similar feature to 8.1.0. The flag is called "auto-disable-minutes", and would disable the field automatically after the elapsed amount of time. It then has to be re-placed or manually enabled again. Donations are welcome either way.