Help with multiple masks

hiya folks,

another noob here with a question about using multiple masking layers.
Firstly, can you have more than 1? I followed the tute at but am wanting to add another mask layer (mirrored so-to-speak). When I follow the tute at the link above all works fine till I try to add another mask layer, only 1 actually shows up, o.O any ideas? TIA :puzzled: