Making a natural !?!? pond

I live in Suffolk where most of the ground in heavy clay. It is the county with the most natural ponds in England. I would like to put a pond in the garden but without using liners or plastic mould. The pond would be around 10 yards square so not small. I would hopefully rely on the clay soil to stop the water draining away. Is this realistic or would I still need to lay something down first?

 

Ive built one before like this, Basicly just dug down to pudling clay then compacted it by running a 3.5 ton excavator across it and pressing it with the grading bucket.

Remember to slope one end gently so as wildlife can drink and you can get the excavator out!

 

http://www.stroudvalleysproject.org/CamPeakPond.html?name=CAMPOND
Our pond was empty within weeks when the livestock were moved away.The clay dried and cracked at the waterline because the Cow's hooves had kept it puddled as they drank.