I live in the basement unit of a house and I rent out the upstairs to skinny young adults and if you heard the stomping around that I hear you would be convinced they are all 300+ pounds upstairs. 

And that full grown Labs are over 20 pounds? 

I'd tell them to pound sand, personally.

Said it was just him and a seven pound dog and seemed like he might make a good tenant.  

This chart says a 75 gallon aquarium weighs 850 pounds when it's full:http://freshaquarium.about.com/od/aquariumsandstan...So, I'd argue that the weight alone, could result in extensive and expensive damage to your floors/flooring. 

The tenant had been complaining about a fear a branch from the tree might fall on her 5 pound dog. 

I rent where animals are allowed, and I got a dog that is under 25 pounds, which are accepted everywhere that allows pets - especially so nobody knows she's a service animal.Because my dog is my service animal, though, I don't have to pay the pet deposit. 

I've installed Adura LVT by Mannington in our home and it has withstood our 5 year old, a 70 pound lab and a crazy pitbull with NO signs of wear at all!

My primary care physician wrote a letter explaining why my dog would help me live in my unit more comfortably, in spite of my disability.The place I live in, however, does accept dogs, and my dog is only 22 pounds.  

They must have renter's insurance, no pit bulls , etc. max of two pets, less than 25 pounds.