I've tried the straw thing too and not had much success, it has to be barley straw though, apparently it doesn't work with wheat or any other cereal. Do you know if the pond had fish in it before? this might have reduced the numbers of natural organisms that eat the weed so with time numcers of beetles etc will build up and may help reduce it. I have a very similar problem, always have done since i had a pond so if anyone else has any advice it would be greatly recieved!