What a lovely environment for your ducks!
I have muscovies: all rescues that for various reasons didn't make it with ducky mama in the wild. In the wild, the mother lays a large number of eggs but there is a very high loss of the ducklings. I visited a muscovy family on a pond near me last month to see how they were doing. The first time I spotted them the drake was with the group keeping a little watchful eye and chasing off other drakes that were coming over threateningly. There were 7 ducklings. A week later there were 2 and after another week later they were gone.
There cannot be a safe way for your muscovies to brood out round your pond. Predators will be able to get to them. The only way to make it anyway safer would be to have an island in the pond for the ducks to brood on and even then, a hungry raccoon can swim. Can your muscovy fly? (My female can but I dont know if my males have useful flight as they dont try and fly away but I doubt that my larger drake can fly).
Where are you? What are the main predators? If you have hawks or owls, planting shrubbery for the ducks to brood hidden within might help reducingn attacks. Clumps of tall native grasses might help -- wild muscovy near me like sitting in clumps of muhly grass -- but grasses will also provide hiding places for predators
The most safe way for your muscovy to brood their eggs themselves would be to have nesting boxes inside a duck coop that can be secured from dusk to dawn. My muscovy use old wooden drawers as nesting boxes. Some won't use nesting boxes but in a secure coop they would be safe brooding in a corner