Tenant has reoccurring overnight guest with a dog

[Marshall Rousseau]

how would you handle this?  I am renting a small stand alone unit in close proximity to other units. Under the lease, no pets are allowed. I also live on the property so have a pretty good idea of what goes on. A tenant texted me and said their "friend who owns a dog is coming to visit. Is that okay?" I inquired further and its a medium sized dog and their fried would be coming over to stay the night one to two times a month. although I wouldn't have any issues with a one time thing, I'm not wild about the reoccurring aspect of this request.  How would you guys proceed?