This sounds like a really interesting project in that location, and must be something to look at. And it sounds like you've tried a lot of good approaches to curing your squash problems. I go some years not planting them because I get tired of the number of problems I have to solve with them. (I have a couple of zucchini in the yard now that may have the borers. I need to get a syringe and inject BT into the hollow stems, a Howard tip from a few weeks back).
The only other thing I can think you might try is dancing around the garden naked under the full moon.
(I know, I know, this is a totally silly suggestion, but sometimes you try everything that makes sense and reach a point where you feel like trying something totally outlandish).
Good luck! I hope you'll post some photos of this interesting pond garden of yours.