I moved to Finland with my seven red-eared sliders last year. The ground is hard and rocky so I hit on the idea of using an old boat as a
pond that could be easily emptied before winter. I put a plug and drainage hole in the bottom and attached fencing around it, plus netting on top to protect from escapes and predators. I also put in an overflow hole, luckily, because there was recently really torrential rain and they would have floated out into the forest. There is a 5000 liter filter pump ("Oasis")and they have the boat's wooden seats as basking spaces. I put in a big basin of earth and sand, with drainage holes in the bottom, for the females to lay their eggs. A couple of ramps to climb and that's about it.
Before doing this, I searched the net for info on whether anybody else had thought of using a boat, but found nothing, so thought it worth sharing the idea now it has been tried and tested.
I'll attach photos but must first make them smaller.
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Photos of the boat-
pond