Thanks for the great suggestions - so far they haven't stuck to the clingfilm, but that G4 sounds like an excellent idea for the future.
I refrained from the bog/large margin area when I designed "main pond mark 3" because (apart from lack of space in my tiny garden) there was an unbelievable "wick effect" occurring in a previous design that had a ring of vegetation. There was/is a problem with collecting enough rainwater to keep it topped up in the droughts we have here. So I maximised on water volume instead when I built mark 3 this year. There are small islands in the pond instead. Dragonfly perches take the form of shrubs and long grasses near the pond (I'm so excited - I just spotted a dragonfly nymph in the pond). The pond is new so there is still too much bare soil though - I agree vegetation would have helped.
I may try the tea towel and twigs
My smaller pond is designed for frogs etc - much wilder, more shaded, clay lined, no concrete, mass of vegetation surrounding it - and I can use the hose there occasionally too because consequently there is very little blanket weed . I'm hoping amphibians will breed here in future years.
Thanks again.