AngelFishFan
Aquarium Advice Activist
I tend to agree with CorvusCorax on this topic...
If the freeze line for your area is, say 3ft.....then
having enough (3ft) of soil around the pond would the the SAME as having it "in" the ground.
In ground, you have not only 2-3' of soil around all sides.You have thousands of miles of soil around it. Anything ABOVE the ground will freeze in the winter time in colder climates. I have it happen even at the ponds at work that are 4-5 feet above ground, surrounded by 4 feet of soil and a dura-wall stone terrace/retaining wall.