Doesnt look too bad to me?
I dont think it can be classed as vertical sides either? the sloping shore/edge looks about right for most wildlife.
With regard the clay...the technique is to have it puddled ( as you probably know) i think this involves emptying out water and borrowing a sheep or two...put them in and let them puddle the clay with their hoofs...
other than that im not sure what you want to achieve...the worst possible thing would be to build an ornamental brick or stone edge all round...put in spotlights, koi and a huge fountain in the centre.....yuck..
keep it tasteful and in keeping with a country pub what ever you decide on
