OK, first of all, what always helps is the fact that you will automatically have copyright over your original IP, and publishing it here puts a stamp on it to say you created it first. Just remember to put something like '© the original author of this work (replace with your name). You may not reproduce this work without the author's permission, etc.'.
You will need to lay out the guidelines more than I have. A full example might say '© 2013 by the author of this work. The work author retains sole copyright to his or her contributions to this work. This work may not be reproduced, broadcast, adapted or sold without the author’s permission.'
Anyway, selling is not really a viable choice for first time rulesets. It's much the same way with most crafts; people will buy into you when they know your products are consistently high quality. There are a bunch of sites, such as
Wargame Vault where you can publish your ruleset, setting the price you want.