Daughter has decided she wants to make a big pond (roughly 10 x 12 metres) for dogs to learn water retrieves etc. What is the best and most economical way of lining this.Concrete, pond liner, clay?
Also would it need filtration or anything. Thanks in anticipation

For something that size I'd buid a proper swimming pool and use salt purfication instead of chlorine. Plus you get the added bonus that you could use it yourself when the weather was nice. My sister's labs swim every day in their pool.

Second that, liner is the last thing you want as the dog's claws could easily puncture it when they leap into the pool.

What does salt purification entail?

did a quick google and found this page. These are alternatives to chlorine/acid that is normally used in pools. She had an ozone system in the last house but prefers the salt as the dogs take a lot of water out of the pool when they swim. Ozone systems rely on the water hanging about the pool long enough to be purified. The salt content is very low, nothing like the ocean.

How about one of those wildlife swimming ponds (remember seeing them at the Chelsea Flower Show). Very natural looking and you can swim in them too.

Probably cost me an arm and a leg

I am NOT swimming with the frogs in my pond. Ychh :-D