I have this issue, but the other way around. When I connect my MacBook to the guest network that I set up with my AirPort Extreme base station, I can still connect to the two AirPort disks that are hooked up to said base station. How is that even possible? Does this have to do with the fact that I'm still in my own user profile where the access information is probably stored in my Keychain? Because I can't access those same disks when I temporarily log into the guest account on this same computer.
What I want to achieve is for computers connected to the guest network not to even see the possibility to connect to my AirPort Extreme, let alone to the two disks hooked up to that. Is that even possible at all?