try a ground anchor with a dlock perhaps, something like this
http://www.wiggle.co.uk/p/cycle/7/Kryptonite_Stronghold_Surface_Ground_Anchor/5360009134/
@fredtc started
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try a ground anchor with a dlock perhaps, something like this
http://www.wiggle.co.uk/p/cycle/7/Kryptonite_Stronghold_Surface_Ground_Anchor/5360009134/