You could disable network sharing on your computer. That might work but i have no idea how deep the block would go.
If the router has some form of guest network (would prob be wireless only) that is what i would use. lets them access the internet on a different network, so they cant get to your stuff.
*EDIT* from the ASUS homepage, it sounds like it does indeed support multiple networks. So setting up a simple wireless guest network (secured, naturally) should be no problem