I don't mind if they come look at it, but the open top of a JBJ Picotope seems like it would invite a lot of "Oops! I was leaning over it while you weren't there and dropped _______ in there" (could be anything, paperclips, glasses, eggroll) Also keeps things from being knocked off the shelf above it.
went to Home Depot at lunch, $4 piece of window acrylic, cheap hand coping saw, some sandpaper. Some drawing with a sharpie, some company time spent with the saw (cuts fairly easy, but cut off with a very shallow angle - straight up and down like wood doesn't do it) and voila! Not perfect, but good enough. Figured I would take it off while I'm at my desk, put it back on when I leave:
To address the possibly of warping brought up by a poster, added a rib to the top to stiffen things up! A little sloppy with the superglue, so have some white ghosting on the rib. The straight rib was easier to 'score and snap' than cut - score with a knife & straightedge, put the small end between a door & frame (right up the score line) and bend it over to snap it off.