The problem with steeper slopes is that it will want to migrate to the bottom faster than you'd like. I still stand by the 1-12" rip-rap, but you need something to slow the effects of gravity on the rock. I have steep banks along two sides of my pond and have not added rock there, but I believe I have few choices...

1.) Drive stakes into the under water slope at about 1.5- 2 foot down and then add 10" tall hog/cattle wire (or something to act as a rock barrier like hedge limbs, timbers, or pipe...or whatever). Then start placing the rock up from there until you get well above the water line.

2.) Just add rock where I want it and add more as it moves. At places along my banks, a rather round 10" rock will roll on down into the abyss.

3.) OR, add rock all the way down to where the slope levels out more. The rocks become their own barrier.

All of which are very labor intensive, hence the reason I have no rock there. I would start with the larger rock (6-12") and then come back with smaller rock (1-2" clean gravel). This smaller rock will fill in the voids and help lock in the settling of the larger rock and give extra protection to the exposed soils in the voids.

Fish on!,
Noel