Duck Poop Piling Up?

[10 Baby Ducklings]

Hello, I’m hoping someone has an idea of something I can do. I have ducks and I keep having trouble cleaning poop out of their run. Originally it was dirt, but then I did some research and put pea gravel on it. That worked well for a few months and I would just spray the pea gravel down. Then it started going between the stones and kind of cementing the stones together. So I put a layer of bigger rocks on it and that helped for several months. Now it’s not draining anymore and it’s creating a big muck pile. When I try to spray it, it dissolves and forms a puddle and then just goes back to muck. I had previously put some liquid on it that was safe for ducks and supposed to help the poop dissolve, and it helped, but it is not a cost effective solution. With the days getting shorter and with it getting colder outside, I’m hoping to get this taken care of quickly. Does anyone have any suggestions?