First of all, your pond is probably not leaking. I always tell people that when they call to tell me their pond is leaking.
"Hi Jan, my pond is leaking."
"No, it probably isn't."
"But it is losing water every day and anyway how can you know that if you haven't seen it?"
"I have seen thousands of ponds and am all knowing. Chances are about 99% your liner has no hole in it. Let's troubleshoot. If I have to come over there, you will need to get out your checkbook, so if we can do this over the phone, my advice is free. Which do you prefer?"
"Over the phone."
"OK, turn off your pump, fill up your pond and let it sit over night. If the water stays put, your water is falling behind the waterfall. If you have a spitter, the water is drooling down the spitter and out of the pond. Check your waterfall rocks. Chances are one of them has tipped and water is not going back in the pond, but falling off the back. Look at the water level in the morning and call me back."
I usually get no call back. The pond owner has learned something. Liners rarely leak. They rarely get holes in them unless raccoons have been marauding through the water in search of tasty morsels.
The pond owner finds the wayward rock, tips it back into place and all is well.