Mine is a shallow pond and I like a rocked bottom. If it were 4 feet deep I would not rock the bottom only one or two shelves as I dont believe you would notice it.
That's a good point Jack... I do have some shelves that are anywhere from 18 inches to 2 feet deep. Perhaps some flat stones would look nice to line the bottom of those and some river rocks or gravel to put in between the flat stones. The sun/light has to be just right and the water crystal clear to really notice the bottom of the 4ft section so rocking that wouldn't really be noticeable.