The reason for 3 to 1 is twofold. One is to get deep enough to help reduce weeds the other is so the slope won't be so steep you can't work on it. It is not critical to have 3 to 1 slopes in the pond. On the back side of the dam if you have one you don't want a steep slope. Many don't use a 3 to 1 in the pond. Instead they rim or cut the edge so it goes from 0 to 6 feet as fast as possible. The exception would be places to get in and out of the pond (swimming areas) and spawning areas. I would put some structure at all depths below max ice thickness. Ledges are good for spawning beds and for fishing. Beds can be from 1 ft to 10 feet depending on the situation.