If you really want to keep him, I would give him free reign on a project he wants to do. It can either be related to the company or not, but let him do a side p

If you really want to keep him, I would give him free reign on a project he wants to do. It can either be related to the company or not, but let him do a side project for work. It can be either a week or a month or more if you are comfortable. He is probably just burned out. Really I would just try to get to the root of the problem and see what he wants to change and work with him to get there.