Originally Posted by
pickerel
I used 4x6 landscape timbers from Lowe's...the kind that have rounded sides just like in the picture. Then I lined the inside with vertical 1x6 boards and 1" foam board insulation inside that and along the bottom. The insulation board also gave a softer cushion for the liner. I didn't fill in the 4" gaps with anything on the outside and never had any bowing, but my pond was only about 2 ft. x 6 ft. x 2 ft. deep.
I used 3/8" threaded rod in the corners with a nut/washer on top and bottom to squeeze it together. If you put additional rods along the sides, it would be a good idea to use threaded rod and add other pieces of wood in the spaces so that it can all be squeezed together. It does have to be disassembled one board at a time, BUT if you have enough clearance between your rod and the holes in the boards, you should be able to pull out a rod, swing the corner apart, then put rods back into the holes. That way you could move each wall as a unit. My holes were just big enough to let the rods pass through, so they got bound into the holes and I couldn't pull them out until most of the timbers were disassembled.