Find out what their needs are whether they are being met and how the company can support them. Make it a priority to have the conversation now. What kinds of opportunities, growth, etc. Never assume they can't be lured away. Employees often say that they never hear the words 'thank you' from their bosses.
Genuine appreciation costs nothing, but can yield significant benefits.
You need to let employees know how much you appreciate them - regularly. Recognize even the little accomplishments. Ways companies are recognizing their people more are by acknowledging achievements at work, birthdays, and milestone recognition at meetings. Find ways within your company that will make your employees want to work and succeed. Create an atmosphere that celebrates success.