Pay to get out extra product at the end of an accounting period, and you'll get out extra at the end of every accounting period. That's what you're telling them you want. I've enjoyed over the years listening to sales managers extol their incentive systems. But listening closely, year to year, what I really hear is what was wrong with their last system and why their new system will be the greatest thing since sliced bread. Avoid long-term employees.
Conventional wisdom admires companies who have retained employees for many years.
Trying to retain employees after they've stopped learning is bad for the employee and bad for the company. Bad for the company because it stifles the flow of new ideas, new insights, new views of the changing business environment. Your star employee, once a dynamo, once willing, able and eager to tackle any task, no longer shows that drive. However, it's more likely that he's simply no longer learning at the rate he was. People enjoy best doing what they do best.