  We propose, and constrain with the latest observational data, three
model-independent parametrizations of the cosmic deceleration parameter $q(z)$.
They are well behaved and stay finite at all redshifts. We construct them by
fixing the value of $q$ at high redshift, $q(z \gg 1) = 1/2$ (as demanded by
cosmic structure formation), and at the far future, $q(z = -1) = -1$, and
smoothly interpolating $q(z)$ between them. The fixed point at $z = -1$ is not
arbitrarily chosen; it readily follows from the second law of thermodynamics.
This fairly reduces the ample latitude in parameterizing $q(z)$.
