Bella loves to poo under our bed too! I didn't even realize it was going on then one day I saw her run under there and then run back out looking quilty, and I checked. Sure enough! Tons of poo. Mostly fossilized. Now (like most of you) I have it blocked off w/old stereo equiptment and shoe boxes.
I wonder what makes pooing under the bed so tantalizing? It's like they know we can't see them under there...