At some airfields, you get tiedowns in the grass that consist of some
kind of weight (such as a concrete block or tire filled with concrete)
and a tiedown. Perhaps they aren't much use -- a plane apparently can
still fly with one attached to the tail.

In this month's 'Pilot' magazine (British) under Safety Matters:

Tiedown attached
----------------
AS A BEECH C23 Sundowner took off from Aldergrove, ATC saw an object
dangling from the tail. It was a car tyre filled witih concrete which
has been used as a tie down. The pilot landed safely after a normal
circuit.
During the pre-flight inspection, the pilot had removed tie-down weights
attached to the wings, but hadn't noticed the weight attached to the
tail.

I have to imagine the flight characteristics of a Sundowner with 50lbs
of concrete hanging off the tail had to be 'squirrely'!
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