He keeps going in the same spot no matter what I use to clean. How do I stop this ?

I'm trying to figure out what is going on. I believe my dog is trying to mark her territory.

We let our friend move in with us. He has two small dogs who aren't very well potty trained and do not get along with our dog so he keeps them in his room and lets them outside after returning from work.

All 3 dogs do go outside, and the back room floor where they are let out is being peed on.

My dog does not pee anywhere else in the house. I have laminate flooring and mop with my own mop everyday. Our friend uses his ownmop to clean up his dogs urine. He does not bend down and soak the urine in a towel first. The urine is cleaned only with a mop.

I'm wondering if my dog is only marking where he has cleaned with the same mop he uses to clean up his dogs urine? I'm grossed out. To me it's not sanitary to use the same mop over and over again to clean urine.

My dog is trained to go outside, is she marking her territory because of this? I don't know how else to explain to our friend to stop using this mop. MY FLOORS ARE BEING RUINED!

The mop has his dogs urine scent on it, so to me it makes sense my dog would mark her territory where it's being used. And even if we can't smell the urine a dogs scent is so much stronger than ours.

I need ground to stand on to back up my theory.