I believe most of "those" programs are of the NR/AO variety (rating wise) and I think they also have the "SC" and "N" content tags; although I haven't set the guards on our account... no little ones in the house.
Yes, the adult guard works. The only bad thing for me is that I pick up an independent local broadcaster OTA. There is no information on the EPG so it is always listed as 'NR/AO'. If I lock out skinemax, that broadcaster is locked out too. I just use the four number password, though to get around it.