How do you keep good employees from leaving?

I had my cleaning company for 17 years now. I have had my fair share of good employees. My longest serving couple has been 12 years. Then I had some team members for 4+ years. While I do not want them to leave as it is hard to find good team members with our core values, I find that they do run their course due to the nature of the job.

What have you implemented that helped your business to keep and engage long term good employees?