Forum Please, need help with my banner
 

I just want a couple things for my banner. I want it to fit all resolutions, and I want to make it randomized (show a different banner with each refresh)
I have searched for a random banner mod but they are all too old for 4.2.

Basically I want my banner to act just like the one on this website http://anime-forums.com
my url is http://anime-forum.net
I would really appreciate some help, thanks.