last year i bought this netfloat, and put it four rings deep all round the pond, just left the middle half open, lots of fiddly bits and messing about but got there in the end.
Then waited for the usual visit from the heron, it actally WALKED on the netfloat to the open middle of the pond AND STILL GOT MY FISH. bought a lot of it so filled the middle up too. it was the only way to keep heron out of the pond, soon got all sorts trapped in it and on it, couldnt feed the fish and couldnt see the fish. crap idea, i threw the lot in the bin.
save your money, get some large guage pea netting in black, on poles streched over and around the pond far enough away from the edge so the heron cant reach the fish, it doesnt look too bad really- cant hardly see it. ive seen the heron walking around trying to get my fish but it cant now.
trust me netfloat is not a good solution.