on putting tracks too close to the edge

Yesterday I was enjoying the fruits of my labor by doing some switching on my N scale layout, when the side of my hand accidentally brushed up against a top-heavy "sky box" car, and it (and several other cars coupled to it) promptly fell off the edge of the layout down on top of the staging yard, derailing a bunch of cars in both trains there. It's not a pretty picture, although at least there was no physical damage to anything.

You can see from the above picture that several cars would have fallen to the floor, had I not recently installed a plexiglass guard at the edge of the staging yard. Now, it is painfully clear that I need another guard at the edge of the upper yard. The next picture shows the gruesome incident from another angle, and a piece of plexiglass on the yard lead already begging to be installed.

Fortunately, I had some leftover strips of 2" wide plexiglass from building the water underneath the HO MILW car barge, so it didn't take too long to measure them, drill holes for the mounting screws (very carefully, using a drill press to minimize the risk of cracking the plexiglass), and install them. I use "fender washers" behind the screws to spread out the pressure on the fragile plexiglass. I don't know what took longer, installing the shields, or getting all those cars back on the track!

The glare from the shields is not ideal, but neither was that derailment in the staging yard. Here's a final picture take from across the other side of the layout, showing that you can barely notice the shield is there, and then only if you're really looking for it.