For winter aeration, we place a diffuser (or 2 depending on how much open water is needed) NO MORE than 1/4 total pond depth, and close enough to shore that the open water goes to the shore or at least goes to shallow enough water so anything that might go IN the water with the pond frozen can WALK out.
Critters or humans for that matter that have to climb back up on the ice after falling in might not be able to do so and drown.
