how to make dog stop pooping on the baby's room floor?

about 2 years ago i adopted a rescue dog. he has seperation anxiety bc he was a rescue.

everytime we leave, even if its for 5 minutes, he darts into the baby's room and poops on the floor. its always in the same area.

i dont yell at him anymore, since yelling did nothing and now i know its not really his fault.

but what can i do to stop this before the baby comes? i really dont want to be dealing with the baby then step in unnoticed poop.

i want to buy a walk through baby gate, since the door doesnt latch shut, but hes a weiner dog so i think hed just wiggle himself through the gate.

is there anything i can spray on the floor that might keep him from doing it? anything advice is welcome. he has a pretty regular schedule of going potty outside. he gets rewarded for good behavior, and scolded for bad/ignored for bad (since he seems to do bad things for attention, scolded only when somebody is home).