any suggestions duck run for drainage/smell?

[Klatimer]

Hello everyone,
I wanted everyone suggestions to keep smell down and drainage. Right now I have pea gravel which worked well but I have flakes that have mixed with it which doesn't help. being able to stray the ground and get rid of the feces helps. But I want to keep the flies away, and help decrease the smell. I dont know what to do. I want to switch to sand but I'm not sure.