I built a pond two years ago. I have a gravel edge I made a few mistakes as I had never done one before. I should have made it deeper it's about 18". The gravel falls into the middle so I put rocks around the edge but it still falls in.
I should have made the sides wider..I also put turf around one side..We had newts and toads within about 3 months of it being dug so they like it..