Lease non-renewal for messy tenants

[Kelly McMillan]

I have had tenants for about a year, who I gave a chance despite poor credit and some other background check issues, because they have a verifiable good income.

In general, they are courteous and communicative and even did some repairs out of their own pocket. I allow pets in all of my homes and they have three small dogs - that I've realized are not housetrained. There is a strong smell and feces on the floor during my quarterly maintenance checks, which likely means urine as well. 

On the last trip, they had an unauthorized cat that 'they were watching for his sister' - who lives in PA. And apparently they needed to borrow her giant cat tower too? Suspect. 

This is the first time I've issued a lease non-renewal. Are there any legal issues to be aware of, and do I need to state why the lease will not be renewed?

I don't have anything in the lease regarding violations of the pet agreement. I've considered a fee for the violation, but don't believe I can, since it is not written. I will be sending a letter requiring the cat to be removed.

Alternatively, IF the cat is removed, and because they are otherwise good tenants and pay rent on time - I've permitting a new lease, if they are willing to put down a deposit that will pay for new wood floors and odor removal when they move out. 

Any relevant experiences, or input on this would be *very* helpful!