Macbook Log Off Only in Clamshell Mode

[iPad Retina]

Is it possible for a mac to log off the user only when I close the lid, I want to do this because I usually carry the mac to school, but at home I usually leave it open

Or can you set a location where it would log off if i were to put it to sleep?

Thanks

 

[Erdbeertorte]

I think the only option would be to disable the screen saver and set sleep in the energy saver options to never.