Hygiene and a static run

We have a chicken coop with extended run that goes into a  large fenced in run (about 9 metres x 5). On one side there are trees and the rest is just ground. When we are home we let the girls out into the top garden on the grass.  However, what is the best way of keeping a static run clean and hygenic ?  I poop scoop daily and  I have been using Stalosan .  Is that ok?  Also is it ok to just sprinkle on the surface?  I just think I am not doing enough.  Any help or advice would be greatly appreciated.

a lot of people use bark chips and replace them when they feel its time with a new layer