xsel like a clipboard manager: keep clipboard content for future use

I'd like to run xsel as background process to keep clipboard content for future use. I run it in openbox startup script like that:

-shell
xsel -b -k

But when I select something with Ctrl-C and close original application, there is nothing in clipboard. Also I don't see xsel process in task manager. What I'm doing wrong? PS. I don't what to use parcellite of smth like that. Just simple shell scripts.