Dog urinating

Question
My son has a boxer that was house trained. This dog never urinated in the house until his girlfriend brought her two small dogs over. He was not fixed and her two weren't fixed either and they are female.  I had Bear the boxer fixed this morning and when my son got him home after about 1 hour the dog urinated all over the wall.  The other two dogs are using puppy pads, what ever that is.  My question is this since the girls were not fixed and Bear wasn't fixed and the females are in heat is this why he has started urinating everywhere in the house?  And isn't it confusing for a dog that always went outside to have pads in the house that her dogs are peeing on?

Answer
Teresa;
Yes, when dogs are in heat the males are driven to "Mark their Territory"!
They will definitely need to stay outside, until he recooperates.
Making him happy at this time is the key to your home staying on a normal note.
So, take the Puppy pads and use them in one place away from the household flow.
It will take time to get over his progesterone in his system, and he remembers how to be a male.
So, for now,
Keep him quiet and away from extra stimuli.
Best wishes,
Melissa