I don't have access to my Dbox at the moment, but from memory....
Go into DBox > Service > Bouquet Editor
Highlight the bouquet that contains the Adult stuff, then press the "dbox" button to toggle the function of the blue button (you should see it change at the bottom right of the screen .....I think it changes between "Lock" and "Rename". When it's at "Lock", press the blue button to lock this bouquet.
Go back into the Main dbox menu, and select "Settings" (I think). Somewhere in there is a setting to attach a PIN to any locked bouquets (may be named "Security" but I'm guessing).
Maybe somone online who has their Dbox next to them can add to this?
Lock the bouqet as discribed above. Then go to settings, parental lock, change the pin to whatever you desire, change prompt for pin to on locked bouqets. You will now ned to enter the pin whenever you want to view the channels, enter parental control or enter the services menu so don't forget it. BTW you can not hide and lock the bouqet you can only do one or the other.