Regarding effectiveness of GBH decoys, I have a friend who has placed 3 in strategic locations by his pond and incoming trout stream. Having this many seems to work for him. His pond is very small, less than 1/4 acre; the stream on his property runs for a hundred yards or so.
One live GBH on our 1/4 acre pond doesn't prevent another heron from landing on the opposite side of the BOW. No more than 2 will set down at a time however. Others fly over, circle, then pass on by.
I can't recall how large your BOW is but you could try placing 4 or 5 decoys spread out around the pond, then add to that if necessary. A couple hundred bucks seems like a good investment that would last for years.
