  We report our present status of on-going project on the measurement of the
static quark potential in 2+1 flavour domain wall QCD with various improved
gauge actions and couplings. Lattice spacing determined from Sommer scale on
these ensembles are from 1.6 GeV to 2.0 GeV for $16^3 \times 32$ lattice with
fifth dimension size 8. We also examine size of discretization error from
scaling of a pair of dimensionless quantities, $(r_0 m_\pi)^2$ and $r_0
m_\rho$, and found small scaling violation.
