[vaksel]

Savings is the most important thing...once you have enough savings you can walk out.

If you really want to keep the guy around, make it easy for him to do his startup while he still works for you. i.e. have him spend 60% of the time working on your stuff, and 40% of the time are free for him to work on his startup. If he gets that security he'll probably stick around.

And chances are he'll be able to provide the same amount of productivity during that time.