Can I force password protection of specific apps on the iPad? I am unable to find out how to force the iPad ask for my password when I want to use certain applications (e.g. e-mail)

I want to be able to share the iPad but I don't want anyone to have access to my e-mail account. The only way I can see to do this is to create and delete the account every time I use it, but this is an extreme hassle. Ideally it should simply ask for my password whenever I want to access my e-mail. How can I do this?
That's not a general feature of iOS. You can lock the entire device, but not certain applications. 

The iPad mail app does not have this as a specific feature either - when adding an account you must store the password so it can check for new mail in the background.

There are some third party apps for iPad that require a password to access them but I'm not aware of an email app with this feature. But it might be worth a search.