App to cover in black part of the screen

I would like a Cocoa App that will hide part of the screen with black. The app should : - be monitor / resolution independent : one monitor could have its top 10% hidden, while another monitor would not be hidden at all - by default, it should hide the top 5% of the second monitor (not the one with the menus) - remember the settings when quitting / relaunching - it should be very easy to adjust the vertical level of hiding. How is your choice : with a slider, or by dragging the edge of a black bar - it should be very easy to hide x % vertically while hiding 100% of the display horizontally