We report the existence of regimes of the two dimensional Fermi liquid that show unusual conservation of the spin current and may be tuned by varying some parameter like the density of fermions. We show that for reasonable models of the effective interaction the spin current may be conserved in general in 2d, not only for a particular regime. Low temperature spin waves propagate distinctively in these regimes and entirely new "spin-acoustic" modes are predicted for scattering-dominated

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... re ranges. These new high-temperature propagating spin waves provide a clear signature for the experimental search of such regimes.