Most of our garden railroads use track power.  To provide reliable
operation outdoors, the track must be cleaned periodically.  I have
found that there are many different methods of cleaning track, and each
one has its pros and cons.
    I use brass track primarily because it was fairly inexpensive and is
very robust in the outdoor environment.  Brass as you all know oxidizes
and the resultant film is essentially nonconductive.  All rail materials
are subject to contamination by dust, dirt, grit, and bug deposits.
Ants seem to find rails very handy to travel on, and their crushed
bodies add greatly to the mess we seem to have to deal with.  Our summer
Florida rains add to the oxidation of the rail along with washing dirt
and grit onto our track.
    Another major contaminant of our track is the plastic that wears off
the wheels of our rolling stock.  Between the heat of friction and the
heating of the rails by the sun, the wheels soften and wear faster
leaving a nice insulating deposit of plastic film.  The sun then helps
to bake this film into a material that is hard to remove.  The easiest
way to minimize this problem is to switch to all metal wheels on all
your rolling stock.  Plastic deposits on track can be removed using
track cleaning fluid or smoke fluid.  It may take some rubbing, but
these two liquids will eventually soften the deposits so that it can be
rubbed off.
    Grit on your rails can be handled by any track cleaning device to
sweep it off the rails.  Grit in the points of your turnouts will
prevent them from throwing, or make them partially throw.
I have found that the easiest solution is to used "canned air" and a
small brush.  The air is available at most office supply stores, and in
conjunction with a small stiff artist brush, can easily clean turnouts
of grit, dirt, or stray pieces of ballast
    Leaves, litter, tree sap, bird droppings, sticks, twigs, acorns, and
other trash require removal by hand.  If your ballast is glued down, a
leaf blower works wonders along with a large wet/dry vac.  I use both
before any operating session, since my layout curves around a large
live-oak tree.
     Oxides on the track must be abraded off to promote electrical
conductivity.  This can be done using any or several pieces of equipment
that are available commercially.  Most of us have used the LGB track
cleaning block which is expensive, but does a good job of removing
crud.  It's use requires a great deal of "elbow grease" when track is
extremely dirty.
Several years back, I bought an aluminum car with one of these blocks
mounted on it which was to be pushed around the track for cleaning.
This worked well on fairly clean track, but was not effective on
extremely oxidized sections.  The car also had an attachment for a video
camera, and was more effective for photography purposes than track
cleaning in the outdoor environment.
     LGB makes a track cleaning locomotive which works quite well
providing you have excellent electrical conductivity between your track
sections.  It has two motors, one to move the loco, and one to drive the
cleaning wheels.  It is a "power hog", and will not run in a section
that has weak conductive rail joints.  The replacement pads are
expensive, but are fairly easy to change.  This unit does not run well
over turnouts, re-railers, and crossovers because it has a tendency to
bounce when it hits the shallow flangeway on these track parts.  Because
of this, you will have to clean these areas by hand. The advantage of
this cleaner is that it does seem to do its thing on your railroad while
you are free for other tasks.

The Aristo track cleaning car is a bobber caboose with a weighted
Brite-Boy pad dragging underneath.  The car has tremendous drag, so it
should be run behind a locomotive by itself.  It seems to take about a
dozen passes to clean the track.  The pad has to be cleaned often, but
this is easily accomplished with some rubbing alcohol and a rag.  Some
Railzip or WD-40 on the leading edge of the pad will increase the
cleaning effectiveness, but will cause the crud to build up faster on
the pad.  I have found that attaching dry wall screen to the pad makes
it a more effective track cleaner.  The downside of the car is that it
will snag on all of your Kadee magnets, and will hang up on LGB
uncoupling ramps.
    When track is really dirty, the god old drywall sander is the weapon
of choice.  It is also called a pole sander, and can be purchased at
Lowe's or Home Depot.  This device will shine your track on one pass no
matter how cruddy it is.  One of it's main advantages is the task can be
performed while standing up.   It is possible to mount other abrasive
pads to the drywall sander.  A 3M ScothBrite pad (green) or 3M Metal
Finishing Pad (brown) will work as well.  I have found that the fibers
from these pads get hung on track joints, switch points, and other sharp
edges.  The drywall screen does not seem to have this problem and is
very tough.  In spite of the abrasiveness of the drywall sander, it does
not damage your track, and is the quickest way to clean large sections
of track with minimal muscle strain.
    My personal routine (if my track has been sitting for a long period of time) is to first run the leaf blower and shop vac to get up all the debris, then use the pole sander to thoroughly clean the track, touch up sidings and turnouts with the LGB track cleaning block, clean out all turnout points using the canned air and a stiff artist brush, and then run a train around with either the Aristo track cleaning car or the one I have with the attached track cleaning block.  A lot of initial work, but a guarantee that your trains will run.