COWS. I recall it was Tom Knauff who wrote that you could begin to
see the legs of a cow at 1,000' (300 meters) AGL.
I also use seeing the tires on a car, tractor or glider trailer. It
takes practice.
Lacking cows or vehicles you can correlate the TLAR ("That Looks About
Right") method with your altimeter on every pattern you presently fly
in preparation for XC / off-airport landings.

Also practice estimating altitude at different airports / landing
fields, and in different lighting / visibility conditions. You might
use a motorglider or airplane to fly to nearby airports and learn to
estimate 1,000' AGL. Take along a current aero chart so you know
those airport elevations and for obstacle / terrain clearance.

Landing on a field or gliderport next to a ridge is interesting, such
as on Harris Hill at Elmira, NY. You need to get down relatively low
on the adjacent parallel hill on your left downwind pattern then make
a close-in base to final over another hill with trees. Good fun. All
eyeball / TLAR in relation to your touchdown spot. Altimeter is not
the primary tool here. Indeed, it is a fairly unreliable instrument.
Use it to verify what you see, but be suspicious of it. Pressure
changes and lag can make it indicate inaccurate altitude.

Then there is the ongoing debate as to setting of the altimeter before
takeoff. Zero or field elevation (or correctly, the reported
pressure.) Read CFR 91.121.
Setting an altimeter to Zero may make it easier to teach a student
pilot a rote pattern that is OK only for that airport, but not ideal,
and depending on your interpretation of "cruising flight" in CFR
91.121, probably not in compliance with the regulation.

So I teach pressure / field elevation for altimeter setting, and make
'em do the math to determine height Above Ground Level. Essential for
XC flyin' and anywhere topography is not flat.

We start our landing checklist at 6,000' MSL over the airport at
Marfa, west Texas (MRF field elevation is 4,850' MSL) near the Davis
Mountains (8,400' MSL).
Visiting pilots taught elsewhere to set altimeters to zero have a heck
of a time with this reality, so I do covered altimeter training and
checkouts. And we have a nice large herd of cows on the grassy
plateau around the airport. No oil beneath this part of Texas -- just
water.

Burt Compton CFI / DPE
Marfa, west Texas USA
www.flygliders.com