Sound crazy? A little! Here's my problem/idea.

I have a 1500 gallon hobby pond on my property, and I also have two ponies who usually remain in their own paddock but come out a few times a week to mow (an extremely efficient method, I might add!), my problem is that the ponies LOVE the pond and for the second year in a row, have pawed a leak in the liner before the end of the summer. ;-(

My pond is very well balanced with plants and fish and very clear water and in watching the horses, it's clear they much prefer the pond water over the water in their frequently dumped and refilled stock tank.

Could I solve the liner problem and save me trough cleaning work by creating a little ecosystem in a giant trough? How large would a trough have to be to keep the water clear and healthy? (And support my 10 or 12 3-4" long goldfish)

I currently use a 1400 gph pump that pushes the water through a huge tank of lava rock, and also have a UV filter which I only used for a few weeks in spring this year.

If I lift the pond above ground, can fish co-exist with a trough heater? (I don't think a pond heater works quite the same- a trough heater has super hot coils that heat the surrounding water to 50 degrees and then shut off)