Pay people that want to leave is better than to pay people that don't want to leave...
What steps to take for the practice
I see people staying in jobs for too long, just because it is scary to give up your job before you have a new one. As I was taught: never throw away your shoes before you have a new pair (wondering if that's why I've got 20+ pairs right now...). As a company you don't want money to keep employees hostage, you want them to want to be there, and if that's not the case anymore, to make sure they feel free to leave. So a practice to get this arranged is to have an extra salary paid out when people decide to leave. We payout 2 months, but of course, you can experiment with that, maybe have it depending on years of working with the company.
The result is that people are more comfortable to follow their instinct, speak out their doubts and decide on leaving.