Protecting a file

[Covert2String]

Hi there, this time I have a more complex question <!-- s --><img src="{SMILIES_PATH}/icon_e_biggrin.gif" alt="" title="Very Happy" /><!-- s --> .
I need to protect my application. If anyone could explain me how I can avoid external manipulation of my app (I'd need a whitelist, though). This is really important! <!-- s:| --><img src="{SMILIES_PATH}/icon_neutral.gif" alt=":|" title="Neutral" /><!-- s:| -->

Thanks in advance

Edit: The best thing I can think is something that completely blocks manipulation like injecting a dll to the .exe and then a simple blacklist.