Check the city zoning ordinance(s) regarding poultry. Some cities have 'em, some do not. Some cities will allow, some cities do not enforce and some are strictly banned. Depending on your local ordinance, that's what the landlord will have to enforce. So if you are in a banned chicken city, there is little hope to write this into your lease.
Further, as a land-owner, I would not wish tenants to have chickens. You should see the 'damage' my hens have done to my landscaping. The fact they are only out free-ranging when I can be around is also a point. Neighborhood dogs can kill a chicken because they are 'playing' with it - until the chicken dies. So if you are in an area without a lot of fencing, you will need to provide protection for said hens - which means fencing, post holes, etc. These items are generally not removable easily (or if they are, are the chickens truly protected?). Yes, you can have chickens in a portable tractor (a coop and run attached together that moves around the property), but it only took our 6 hens 3mo to eat/scratch up/poo killed the grass in the backyard. If the compost heap which houses used bedding isn't folded regularly, the flies become a problem as well. But I have horses next door, so it's hard to determine the source of the flies - our broilers catch the flies to eat as extra protein!
