At that scale, you will have to be an obsessive neat freak
to keep it running. Unless it is completely enclosed, like
in a greenhouse or something, you will have to contend with
all kinds of flying and crawling mammals, birds, and insects
as well as weather and the plants themselves. Even a stray
blade of grass would have the potential to stall a train.
I think most of the garden railroaders will tell you to go
"O" or bigger.

But if you insist, you might want to look at some of the new
vinyl products designed for outdoor deck and fence work that
machine like wood but are mostly impervious to rot, mildew,
etc. Maybe 1x4's half-lap jointed on a bed of compacted sand
like you would do paving bricks and secured with gutter spikes.
And I think I would be inclined to try tiny screws instead of
nails as less likely to work loose. And if you insist on the
"quiet track" thing, maybe try micro-mesh packing material
instead of cork. Or maybe something rubbery like bicycle
inner tubes. Outdoors, I think I would rule the noise factor
irrelevant and go for solid mounting, but it's your call.

Mounted to a solid base, your track will take more abuse
than you might think. It will probably support your full
weight vertically in sneakers if you don't scooch around.
You can protect it somewhat by building up the surroundings
flush or slightly above the top of the rails, although that
might detract from the esthetics of your layout, depending
on your scenic plans.

And if you *really* want it to be sturdy, you can make your
own "track" by embedding metal strips in the dielectric
material of your choice, pour a reinforced concrete base,
etc. From an engineering standpoint, just about anything
can be made to work with sufficient investment of time and
materials. As a hobby, it's up to you find a performance
vs. difficulty tradeoff point that fits your comfort level.

In article 4m_Kd.74$Xs6.26@trnddc01, says...
I'm thinking about putting an HO Scale railroad in the garden when I
plant it this spring. I'm posting here because I need advice on what I
can lay track ON that would be sturdy and not harm my tomatoes,
strawberries, watermelon, carrots, green beans (or whatever else I plant.)

At the moment, my main question is how to securely mount the track. I
plan on soldering every joint so electric connectivity isn't a problem.
The track is about 1" wide with plastic "ties" between the rails.
Normally, track is mounted by putting a nail through the center of the
tie in to a board or with glue. However, a 1/2" nail like I use
wouldn't be sufficient to hold track in place on dirt/weed block.

Also, HO scale track is somewhat fragile. Any ideas on how to prevent
having it stepped on? (I'm sure many gardeners have come across a
similar problem.)