I've changed the edge of my pond, which has involved digging up to a foot wider than it was and putting some rocks inside the pond edge that weren't there before. When I fill the pond up, the water level drops by about an inch so I've got a hole somewhere. I've checked the obvious places and made sure the edge is high enough. All that's left is that one of the rocks has nicked the line somewhere along the way. Are there any tips or techniques for helping to find the hole other than working my way around the waterline to try and find it? In doing this, I'd have to remove each and every rock as I went round until I found it. Any help is appreciated, as always.