When does Hank normally poop? What time are you usually taking him outside?

And is that time delayed on the nights Mike comes over?

It is hard to imahine this happens "every" time, because Hank has to need to go to do it in the house. Take him out for his walk at the normal time, with or without Mike. Take him out for an extra long walk just before Mike arrives. Point being, get Hank to do his business before Mike arrives, he won't be able to do it when Mike is in the house.

And THEN it will be interesting to see what he comes up with instead!