Having located a number of ideal glacial stones/boulders of a similar size, shape and colour (see Suppliers), the next task was to drill 6 stones to sit on the steel rods. I was rather nervous about this and bought 2 or 3 spare stones in case of shattering.
In the event, there was no problem. The original idea was to use a diamond core cutter, but this turned out to be quite slow. So we tried an SDS+ hammer drill, starting with a brand new 8mm bit and then progressing through 10, 12, 14 and 16mm bits until the holes were large enough to take the steel rods without sticking (the ribs on the 12mm rebar meant that 14mm was not quite enough to avoid possible jamming which would have made repositioning difficult).
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