  We describe a new mechanism to continuously protect alkali-metal atoms from
spin relaxation using a single off-resonant optical beam. We experimentally
demonstrate that state-selective light-shifts can synchronize the Larmor
frequencies of the two hyperfine manifolds, and by that form a unique
decoherence-free subspace. We report an order of magnitude suppression of the
spin decoherence for cesium atoms, simultaneously protecting from random
spin-exchange collisions and partially also from spin-relaxation by the
interaction with weakly-depolarizing walls. We further report an order of
magnitude improvement of the quality factor of the magnetic states. Our results
demonstrate the ability to use the multi-level structure of atoms or molecules
with accessible optical tools to engineer useful decoherence-free subspaces.
