Keep them motivated, working on interesting things, help them continue their growth even if that growth means they're leaving the company. And the harder part in some ways... tell them your own aspiratations for growth and the potential for you to move up (and/or on) yourself.
Definitely good old Google Alerts is key. Also, social media monitoring with Social Mention. Key: Read their blog.
For product updates; keep tabs on their website changes with Visualping.io.