There are several things you can do to keep the smell done. Firstly, attack the smell at it's source!! You can do this by adding Bokashi bran into their feed. This results in a firmer formed pooh(sorry for being specific) and cuts down the smell by at least two thirds. Secondly, you can add Garlic(from a horsey store...not supermarket) just half a teaspoon to each feed, as this will also cut down the smell. Aubiose/hemcore is brilliant for cutting down smells...again supplied by any horsey store. Also, you can sprinkle Citrenella and euycaliptis(ca'nt spell..tired) onto the hemcore. This stops flies entering the runand gives their bedding a lovely fragrance. Hope this helps.
Also, if your hens are going to be kept in the run most or all of the time, each evening, just go around the run, picking up the hens' droppings. I have also found that often the smell is coming from unexpected places.......like their water!! During hot weather it soon becomes smelly, as the hens dip their dirty beaks into the water after eating, so there is a residue of food left.