Set your router to use openDNS and then use that as a filter, it can block categories and then blacklist/whitelist specific sites.
Of course this won’t help if the iDevice is taken to another wifi network. If you really want full control then block the app store and Safari and use k9 browser. Of course you can just go to your “shomer” every time you want to access the app store and have it temporarily enabled. Annoying true, but if that is the control you want, you can’t have your cake and eat it too.