[xmonad] How to make a window floating above all the other windows and border-less?

Hi, I felt that a digital watch at the corner was so in-noticable. So I planned making a clock watch, just three handles, transparent background, in the center of the screen, floating. But I met a few problems here. I made the windows "over-redirect", so it has no border. Well, how to make it floating above all the others then? Normally, I could do this in xmonad's config file, to make THE window floating, which also is above all the other windows. But with "over-redirect", it does not work.... -- 竹密岂妨流水过 山高哪阻野云飞