Nothing you can do about subtle tanking, but playing turds over studs can be corrected by the commish if there isn't any injuries at play, so can playing players on a bye or injured. I'm against all-play because it takes some of the fun out of the game. In the leagues I commish everyone knows I require them to play their best players (you know it when you see it) and I will substitute out injured players or players on a bye if they forget. It's more work for me to monitor lineups on Sunday morning, but it is working for our leagues. The main thing is that everyone knows where I stand on tanking and I wouldn't hesitate to replace an owner that doesn't comply and has already been warned.