mdrum
It would be better if you specify more fully what type(s) of Internet access you want to stop, ie what you are trying to achieve in a practical sense, rather than proposing the answer.
People here could advise you more effectively then.
It would also help if you tell us what mode your sme server is in ie gateway & server, server only, & a description of your home network arrangement, are you using a seperate router & firewall etc ?