Remember the sides of baths etc are steep and very smooth, not good at all for critters to get in or worse still- out of your ponds! think hedgehogs falling in? frogs getting out.

The pond would need to be 18" deep or so, this is to do with it freezing in winter, creatures who live in the silt will not want to be in-tombed in ice, and you will need to clear a breathing hole for the gases to escape should it freeze.

We have a small pond and I love spending hours just watching what goes on....roll on summer!