Our pond was located so that the lowest spot is in the back corner where our land slopes down away from the pond.  We designed the pond to overflow at this location when the water level rises, making sure the water will not rise above the stepping stones at the very top.  The white pipe shown in the photos below is our pond filter drain which was also directed toward this location. To take advantage of this situation, we built a bog garden here and planted perennials that like to grow in these conditions.

 We dug a wide hole no more than two feet deep and lined it with heavy plastic.  The top of the bog is on a slight slope so that water will always move away from our pond.  We then stretched the pond liner up over the edge and down this small hill so that it ended over the top of the plastic.  

It is important to be sure the water will flow freely from the pond and as far away as possible.  If the drain does not direct the water away, it could flow back toward the pond and become trapped underneath the pond liner.  I have read accounts of pond liners pushing up from the bottom because water was collecting underneath and pushing the liner right back up into the water.  For this reason, we made sure enough liner was available to pull it out of the pond and down into the bog area.

We used a pitch fork to poke holes in the plastic bog liner that was furthest away from our pond.  We then filled the bog garden back in with good quality garden soil.  The bog garden soil will now hold more water and remain moister than other areas of our yard because of the plastic underneath the soil.  Poking holes in the plastic allows it to drain slowly so it does not completely fill with water.