Up around my area in NorthEasyt Victoria on the Chiltern rutherglen deep lead system they would put down a series of Bores across the valley to locate the deep lead gutters and the rising bedrock. Perhaps try using a 4inch hand post hole auger and a couple of extensions to test the dip of the ground. This should save you a few blisters as long as the ground isnt too rocky or hard. :argh: 
