Space limitations may tempt you to run the track close to the edge of the benchwork. Doing so could allow for an extra track, but the big risk is that your prize loco could end up wrecked on the floor.

The accident might not be the result of an operational derailment.  Instead, it might simply be because someone caught the train with their elbow, or perhaps an earthquake shook it free.  When gravity comes into play the only direction is down, and the only thing stopping your loco will be the solid floor which could be several feet away.

Trains generally look longer when they disappear momentarily behind a tree, some vegetation or a structure.  Where feasible, try and move the track at least 2-3 inches back from the edge of the benchwork and add some small obstacles between the track and the edge.  Use some well-glued miniature bushes, a small slightly raised bank, a robust fence of some kind, or some clear acrylic plexiglass to form a physical barrier.