  A challenge in precision measurement with squeezed spin state arises from the
spin dephasing due to stray magnetic fields. To suppress such environmental
noises, we employ a continuous driving protocol, rotary echo, to enhance the
spin coherence of a spin-1 Bose-Einstein condensate in stray magnetic fields.
Our analytical and numerical results show that the coherent and the squeezed
spin states are preserved for a significantly long time, compared to the free
induction decay time, if the condition $h\tau = m\pi$ is met with $h$ the pulse
amplitude and $\tau$ pulse width. In particular, both the spin average and the
spin squeezing, including the direction and the amplitude, are simultaneously
fixed for a squeezed spin state. Our results point out a practical way to
implement quantum measurements based on a spin-1 condensate beyond the standard
quantum limit.
