Re: Pond shelves are too shallow
#2
Although not able to your question, I think your pond looks really lovely (and I'm not noticing the pots for the plants apart from the edge of one on the LHS which to me looks perfectly fine and providing a nice contextual frame to the pond).
In my small tropical fishtank, the only species of plant that I've been able to keep beyond ~3 weeks has now lasted for 3 years - but only because I keep them in terracotta pots which helps keep them upright. Others may think this looks ugly and unnatural, or may think the nerite-snail eggs covering all the pieces of wood is ugly, but I'm happy with it because the actual amazement and joy of keeping a plant alive for that long vastly outweighs its aesthetics.
I do hope that someone will be able to advise on plants that do better for your pond. If not, though, then perhaps it might be worth looking at the UK Aquatic Plant Society website.