Tenant demanding grass for yard

[Jenny Adel]

I've got a tenant in a single family residence who has been extremely aggressive and demanding since moving into the home a few months ago. We re-did the house and it's in great condition- new appliances, new paint, new bathroom, working AC and plumbing etc. Very clean as well. The fenced in backyard had sparse grass when they saw the property and signed the lease. Lawn care is tenant responsibility under our lease terms. They have kids and 2 huge dogs and she's absolutely furious that the yard is muddy most of the time (lots of rain in Oklahoma recently). She is saying that they pay for the yard and that it's uninhabitable and that we are discriminating against them by telling them we won't lay sod. (They looked up ALL of our other single family homes and are saying that since those yards are better, that we are mistreating them). Here's what I found under OK Landlord tenant law and wanting to make sure that I'm reading correctly that I'm not REQUIRED to give them grass;

§118. Duties of landlord and tenant A. A landlord shall at all times during the tenancy: 

1. Except in the case of a single-family residence, keep all common areas of his building, grounds, facilities and appurtenances in a clean, safe and sanitary condition;

Would love some input here! We don't want to be cheap landlords or anything (the house is in perfect condition on the inside), but I also don't want to be bullied into giving them something I'm not required to. "Give them an inch and they ask for a mile...."

Thanks for any advice! I'd also love ANY input on effective communication with difficult tenants. Don't want someone bashing in walls out of anger!!