Let me offer a hybridized suggestion.
Keep in mind as you read this that I tend to be a bit ruthless when it comes to guild organization and discipline so it might seem rigid.
Set a rotation up. Say you have 4 mages and 2 slots for mages in your 25 man.
Month
Week 1 Mages on: Mage1 Mage2 Sub: Mage3 Off: Mage4
Week 2 Mages on: Mage3 Mage4 Sub: Mage1 Off: Mage2
Week 3 Mages on: Mage1 Mage4 Sub: Mage2 Off: Mage3
Week 4 Mages on: Mage2 Mage3 Sub: Mage4 Off: Mage1
Give DKP to the mage who was on as a sub as if he participated in every boss kill. Expect that every so often someone is going to miss. Thats why you have a sub. And guess what, if one of the other classes is light subs will wind up in more often then they realize because life is life and shit happens.
It is important that the person who is on sub duty understands he needs to be geared and specced and ready to go as if it was his on week, even if he doesn't go. He can play an alt or whatever but listening in on vent or guild chat and being ready to go if someone needs to drop due to power, or other assorted life emo crap. It also gives you guaranteed time during a month when you don't need to be a slave to your guild.
Remember, the 3 most important points to having a happy and healthy raid team:
1) Everyone has fun.
2) Everyone can participate.
3) Everyone can measure their contribution.
As long as you meet those 3 points, everything else will fall in place. Those who suffer from a lack of skill (Not a lack of gear) will make themselves apparent, and so will those who don't attend enough. Some times you have to make the hard decisions for your raid team. He's my friend but he's been out with no notice for the last 3 weeks yet he always finds time to PVP.. time to get moved to "Friends and Family" status.
Your raid team needs to understand that while this isn't a job, or the military, they are responsible for 24 other people that night and they owe the raid team an explanation if they can't attend. BTW: I feel like going out to drink with friends is a perfectly valid explanation every so often.
As a raid leader, you have responsibility for setting the dates and times of your raids as well. Your raid team needs to know: We raid, Sunday, Monday, Thursday, Friday from 8-12 SHARP. Invites go out at 7:45, replacements come in at 7:55 (for example). If they can't meet that then they can't raid with you. As a general rule, I suggest that you avoid taking people who can make a couple nights of your raid schedule but not others for long periods of time. That is NOT fair to the rest of your team and as a raid leader your primary responsibility is to the TEAM, and not to yourself.
I know this was long winded, but I hope it helps you out.
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