this idea was posted here by someone years back: let the pond leak until it
stops (sounds like you already know where that is....) make some kind of
mark or line somewhere at the surface. add just enough water to bring the
level back up a quarter inch or so (depends upon how fast the leak) turn
off all filters, airstones, waterfalls, etc to allow the water to be as
calm as possible. go around the edge of the pond, and very gently drip
some milk close to the edge, a little at a time, watch whether or not the
milk gets sucked towards the liner, and it will show you where the leak
is. for quick patch, you can use a swimming pool wet/dry patch... when
there is time, patch tape inside and out will do it. I also cover the
patch tape on the outside with the stronger tape made for joining two
liners.

REBEL JOE wrote:

I have a leak in main pond its about 10 inches down. Water goes to there
then stops so its at least at the top. How in the world do I find it and
what do I patch it with.Please help in a panic here.

http://community.webtv.net/rebeljoe/POND