Roll away the stones

One thing for sure - the soil where I'd remade the pond edges was definitely firm enough to put down the underlay yesterday - it was frozen solid as it plummeted to -7C the night before last.  We laid the underlay out - me in my socks so as not to get any mud onto the newly laid fabric - result = cold toes.  Then: how to lay the 7mx6m liner without dislodging the underlay but ensuring it goes right down into all the corners and with sufficient overlap at the edges?  We rolled the liner up from each edge towards the middle, put the ensuing sausage parallel to the patio down into the contour of the pool and then unrolled it back towards the sides.  Then we rolled the edges back under the underlay to try to stop any stones rolling down between the liner and underlay.  The simple instructions in the pond book 'weight down the edges and ease them as you fill the pond' miss two really key points.  Firstly, you can't do that if you have a bog garden as well as the main pond.  And secondly, we haven't dared put any water in it - last night was even colder, nearly -8C this morning.  You can see the frost on the liner!  So when it thaws we'll put a bit of water in the main pond and tuck the corners tidily, then let it fill up over the rest of the winter. We'll pump the bog garden (on the near right) out into the main pond to check and set the main pond levels, then fill and set the bog garden level - it will drain out of the back (back right corner in pic) into a rock-filled sump.  Two pipes - one near the patio, one at the far side - allow water between the two sections.  Sounds like a plan, eh?