ESA Question about amending damages section of lease

[Tracie Van]

Writing this from WI.

I have a tenant who told me their DR says they should get a pet. She wants a cat. We've had the WORST luck with cats and damage. Spraying and/or urinating outside the litter box. Two units were so bad that we had no choice but to scrub, treat and put a sealer down over the concrete flooring to get rid of the smell before laying new carpet. Since then, we don't allow cats. 

I know I can't charge an extra rent fee or security deposit but, can I amend the damages section of the lease to include damages caused by pets? Specifically damages to the flooring stating that they would be responsible for the costs of replacing carpet and any treatments necessary to remove odors should the pet urinate/damage the flooring? 

So upset that we have to be forced to allow this. I totally support Service Animals because they are needed and trained but not ESA's because of its rampant abuse.