My favorite way to protect expensive pants is to carry them in my
pannier. If you have to look respectable between the place where you
park your bike and the place where you can change pants, you can wear
your suit pants over your riding shorts.

But if you don't sweat a lot and if you don't mind wearing the pants
out in the saddle area, you *can* buy a pants protector. This is a
sort of half gaiter that you can strap on to protect the inside of
your ankle and shin.

(I'm wearing a home-made pants protector in this pictu
http://roughsewing.home.comcast.net/...S/LINJERSF.JPG
back view:
http://roughsewing.home.comcast.net/...S/LINJERSB.JPG )
(store-bought varieties are only half as high)

If you are wearing black work pants, all you need is two safety pins
and two pieces of tape or ribbon that are long enough to wrap around
your leg twice.

My tapes are three and a half feet long; even if your legs are
thicker, a three-yard packet of tape should be plenty. It should be
half an inch wide, as knots in narrower tape tend to jam.

Sit down with your knees bent and form a pleat on the outside of your
leg. It's easiest to just stick a pin close to and parallel to your
leg, leaving the excess fabric sticking out like wings, but it looks a
little less dorky to smooth the excess into a dart and pin it flat.
The wing method is a trifle more reliable.

Next, smooth your pants upward, stroking any excess fabric to above
your knee, and wrap a tape around your leg in the notch below the
knee. For some reason I've never heard explained, garters *must* wrap
around twice or they won't hold. No matter how wide or narrow the
tape is, it must go around twice. Mysterious, but experience shows
that it's true.

Put the middle of the tape where you want the knot to be, then hold
the ends together and pull to make them even. Cross, bring them back
to the beginning point, and tie a bow knot. (Same knot you tie in
shoelaces.) Tension must be just so: you should be able to feel the
tape while you are tying the knot, then be completely unaware of it
afterward. Be sure your knees are bent while tying the tape: its
purpose is to keep your pants loose over the knee so that they don't
pull while you are riding.

When you get to work, pull both bows undone, use the safety pins to
fasten the tapes together, and put the whole mess into your pocket.

I'm awkward about getting on and off; if I mount and dismount a lot of
times during a ride, the right pin is likely to bump against the
saddle and open. It's best to look down each time you mount and make
sure the pins are still there and still closed. A spare pin in your
wallet is a good idea -- or three or four; safety pins have a lot of
uses.

--
joy beeson at comcast dot net
http://joybeeson.home.comcast.net/
The above message is a Usenet post.
I don't recall having given anyone permission to use it on a Web site.