Keep it as it is but a day only counts when you've logged on and played. So after 7 days that you have played on your merits decay and after 7 days of play you collect any reward bonuses due.
Not a perfect solution but at least then you are not punished for going on holiday, being ill etc, or if you can only play a few times a week.
Not a perfect solution but at least then you are not punished for going on holiday, being ill etc, or if you can only play a few times a week.