Let's go back to what was part of your original question.......What will be the expected maximum thickness of winter ice? I am sure that there are local governmental sources that can answer that a lot more accurately than most of the members of this forum. Two foot thick ice seems considerable to me, but being in Florida, what do I know about it, ice is something WE put in tea.
You may be able to get by with only a small portion of the pond being 3 feet deep. In that scenario, the effects of hydrostatic pressure should be minimal.
Whatever the thickness of the winter ice, keep in mind that a hole must be maintained in the ice for the duration of the winter to allow gas transfer both into and out of the pond's water column.
"Everybody is ignorant, only on different subjects." - Will Rogers