Yeah, that's actually a result of the way they do fullscreen. The proper way to do it is actually making the app fullscreen, the way those games do it is by making a window the size of the screen that covers the menu bar and dock. Programs running in proper fullscreen can't be command-tabbed out of. What you can do, to make the game approximately fullscreen, is open ~/Library/Preferences/com.bit-blot.aquaria.xml (Where ~ is your home directory) and change line 16 (<ScreenMode resx="<yourscreenreshere>" resy="<yourscreenreshere>" bits="32" fbuffer="1" full="0") so that resy=your screen height in pixels minus 44 and resx=your screen width in pixels. This will, essentially, make the game window the size of your screen minus the menu and title bar.