  Polaronic effects are investigated in the two dimensional t--J model
(describing Cu spins and holes of the planes in high-$T_c$ cuprates) in the
presence of in-plane dynamic oxygen breathing modes. We focus on the effect of
dynamic multi-phonon modes. Spin and charge structure factors are computed. We
found evidence for self-localisation of the holes and {\it increased} short
range antiferromagnetic spin-spin correlations between the remaining spins.
This effect persists when all the in-plane oxygen vibration degrees of freedom
are taken into account. This suggests that dynamic phonons could play a key
role in stabilizing inhomogeneous stripe phases or domain wall structures.
