Pet Addendum Help

[Joe Richardson]

I'm closing on my first duplex this Friday and inheriting tenants on both sides. In the south unit the tenants just moved on on February 1 2016. There is not a dog on the lease but the old owner "just found out" they have one. I would like to create an addendum and charge pet rent. My plan would be to have my lawyer involved and so there will be a fee I'm sure. Should the tenant be on the hook for this fee in some way or do I have to chalk it up to bad land lording by the previous owner? Move to the north unit. They have a dog and a cat. Only the dog is on the lease and they put down a $250 refundable deposit when they moved in (for the dog). I'd like to do the same pet rent addendum for the cat. Can I pass along those fees? I'm a first time landlord and plan to meet with the tenants for the first time hopefully this weekend and I really don't want to look foolish. My goal is to set the tone that the lease is king and it's the rules all of us are playing by.