Automatically unmount Samba shared drives when Sleep Mode?

I'm wondering if there's a way to automatically unmount any Samba or external drives when going into sleep mode? When at home I have a bunch of drives mounted so when I bring my Macbook to class and open it up, it gives me a bunch of errors not being able to connect to the SMB server... since I'm not even connected to my home network anymore.

It's a slight annoyance, but it's really getting on my nerves after a year of it - having to click 'ok' a couple of times every time I leave my house.

Thanks!