I have a combination of trim and coverings around my layout along the viewing aisles:
I mounted vertical sheets of 3/4" plywood, painted green, to provide a barrier against children reaching or crawling underneath. Each is held in place by two "carriage-bolts" which I can remove easily when I wish to gain access to the storage space behind. These vertical boards are approx. 3" above the layout level itself, to provide a safety edge against trains falling off to the floor.
I used fabric in places where I want quick access anytime. There are shelves and file cabinets immediately behind the drapes . Trim strips and molding complete the tops of these areas.
The short piece of plastic trim seen here
is slightly curved to allow for the swing-open of the cellar-to-garage door (you can see its doorknob in the lower righthand corner of the photo immediately above.)
FrankM
P.S. I admire how beautifully Tom "Gilly" and Mike CT have finished-off the fronts of their layouts. Both are very, very well done, IMHO.
