I've thought about this some lately given the recent events in Dallas.
How would I motivate giant men with giant paychecks? That's a tough one. Fear is a motivator, but what do these prima donnas fear? I guess the one thing the majority of people fear is public scrutiny of shortcomings.
Every player gets graded each game. I would start by informing the team that if immediate improvement isn't shown, I will post all grades in the locker room for all teammates to see. Second, if that doesn't precipitate an increase in effort, the grades will go up on the team website for all fans to view. Third, if that still fails, the bottom four players will have to participate in a press conference with news media to answer questions about their performance and the grades received.
I would remind the players that the average NFL career is 3 years. That means 48 game. If you can't give me fanatical effort for the short time you're in this league, you don't really deserve to be in this league. I would inform them that I have a floating 8-person cut-list. I would develop and disseminate a formula for winding up on that list. I would remind the high-dollar players that if I couldn't cut you because of the salary cap, I will deactivate you and bar you from the team and work with Detroit for a trade.
Would it work? I dunno, but it's what I would do.