This is our fifth year with our pond and whenever we have safe ice, it is about 9". I have never seen it get any thicker, which seems strange to me. Lakes near by could have 2 feet, but we still only get 9"!
I always thought it was because we have 46 degree water entering year round. I drilled a bunch of holes last week because we have some bridge repairs to do this coming weekend and the ice will make the job easier. The kids were all skating on it last week-end.
I look for "black" ice as it is the strongest. We have about 5" of it with about 4' of "white" ice on top.