Thanks Blunt, If you do hit rock it may be worth getting a core drill (45mm), drill about 70mm, break it out with a crow bar or chisel, drill again and keep going as much as you can, no concrete needed. That or hire an electric kango.
show us a pic of your work when done. <!-- s:D --><img src="{SMILIES_PATH}/icon_biggrin.gif" alt="

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