Heidi from Heidi Consults has shot from the hip and aimed at every point Mike Sheldon made when he held this talk in Cannes "Why your best talent is leaving and what you can do about it": Now, if you and your award winning team are not in Cannes right now, you might want to read both of these.
The real reason why your best talent is leaving your agency

For anything. Is it because the industry doesn’t want it, or is it because the industry hasn’t created it? There isn’t a person in our industry who can tell you what a Senior Art Director makes. Believe me, I was asked the question many times when I was still recruiting, and because there is no hard and fast answer, I would turn the question around and ask, ‘How much do you have to spend?” and the exercise became finding the best Senior Art Director for the salary available.
If there were salary and title standards, everyone would know what was expected of them to receive the next raise, when the next raise would happen, the next promotion, when the next promotion would happen, and the next level of responsibility. That’s what talent means when they say ‘Growth’. They want more responsibility. They want to grow in their learning and expertise. They want to become more valuable to you. BUT because this is rarely, if ever, communicated, they figure the only way to make more money is to leave.