Agreed that it needs to be dry, and the more air and space the better to disperse the smells.
If the area that they are in is covered, it will help to keep it dryer, if it is in sun, it will help to dry out and lessen the smell.
A few inches of sand, or even wood shavings to make a litter in thier pen may help to absorb moisture. A pile or bucket of sand or wood shavings may be helpful sometimes too to spread/shovel over quickly between your weekly cleanings. (in the circus, they have a person who pours a shovel of sand on elephant poo, until they have time to clean it up properly)
If a lot of animals (of any kind) are in a smaller space, the smell is greater. The more space the less smell. Using close space means more intensive clearning/cleaning on the keeper's part.
There are products designed to regulate the poop (smell and consistency). I have seen one called 'Ultra Kibble' here in the usa and in the Uk 'bokashi bran'. I think perhaps these have a partially drying effect on the droppings. I also sometimes notice a difference when I give my hens treats of raw rolled oats (old fashioned oats, which they love)
Could it be the feed or snacks they are eating?
Wost case scenario may require cleaning twice per week.