There are a lot of experts on this site, but there is also no substitution for running a good old fashioned experiment.
Maybe create one or two BG spawning beds at a site you can easily observe, but doesn't have a heavy human presence disturbing the fish.
When you see BG on the beds there, do a good survey of the rest of your pond. If you don't see any other BG on beds, then you definitely have a lack of appropriate spawning habitat.
Rod, there is more to this than making a bedding area. We can add the best substrate ( of what we understand is the best) and they may or may not use it. Here's the thing.. we may not understand -ever- why they use one area and not another, even though "we" feel the habitat is perfect.
Each pond seems to be different too.. so I don't feel assuming there is a lack of the right substrate is really a complete answer.
If the pond is big enough, and we add substrate in enough areas, chance is there will be more beds (in one area or another) but what we proved is what? If we did the entire pond, they will still only use certain areas and I think I can safely say the fish are the only ones that know why. Last year (winter) I added tons of sand and pea gravel. The area they moved up into got over-taken by Tilapia and the BG were run out. I have yet to figure out where they successfully bedded but I have 1/2' to 1.25" BG everywhere.
