You cannot stop the user from playing around with the developer toolbar, and to be honest that is a very very good thing. I wouldn't want you to take control over my browser, not that I'm using IE, but still.
What you can do however is to tell the browser how it should render your page. And that's what the X-UA-Compatible is for.
Okay so actually answer some of your questions:
Compability view is for sites that are designed for older versions of IE.
Websites that are designed for older versions of Windows Internet Explorer don't always display as expected in the current version. We addressed this in Windows Internet Explorer 8 by adding the Compatibility View function that allows users to "revert" to a previous browser version of the platform, which emulates IE7 Standards mode.
Which you can read in the link provided by @Alesanco.
So what does X-UA-Compatible
do? Well it tells the browser in which mode it should render the page, which means that you can tell IE9 to render the page as if it was IE5.
This means that you can control the rendering of the page to some extent, but you cannot expect to have control over wether the user plays around with the developer toolbar or not, unless you have access to the users computer.
See this thread for more information.