I like garden railways. I even have a G-scale 3 car train that goes under the christmas tree. The problem is that they are EXPENSIVE. Disregarding the cars and locomotives, the track itself is quite pricey. And yet I envision a mass transit system for all the gnomes and elves that live in the backyard. What to do?
First, go check out this guy's backyard monorail:
A model monorail would be great. It could be suspended from the trees where available, and require only a few supporting posts where trees are not available. Plus, with only one track, you eliminate the problem of trying to build double-track that maintains a set distance between the rails.
The plan is to use flexible copper tubing for trackage, which should be fairly aesthetically OK, especially after it oxidizes. The monorail itself will be a suspended type (under the rail), unlike the Disney top-of-the rail type. Track costs should be minimal. Control will be radio control and onboard batteries, so nothing will have to be electrified. I can see a station on the deck, a station in the woods.... I can see all kinds of things.