When I was a manager, I had a rule that all my directs had to always be looking for new opportunities. If they find something better, I wanted them to leave. It made sure of 2 things for us: 1. We knew that anyone could leave at any moment, and we always planned accordingly. 2. We knew we had to keep people happy. If someone didn't like something, we had to change if possible or that person might leave. Conversations about having interviews and being contacted by recruiters became open, honest, and casual. There was no fear about someone might find out if you were looking, and people shared what they found out about talking to potential employers.