My dog spends a lot of time with my father in law at their house. Lately he's been pooping on the back porch even though he's just been outside. Recently he started peeing too. He doesn't do that when he's home with me. He's bonded with me and with my father in law when he's with him and we've discovered that it seems to be when my FIL is away. We think it may be anxiety. Thoughts?

By the way, he's been going back and forth between houses for about a year so that he doesn't have to be crated when I'm gone. (My father in law thinks it's cruel despite my best efforts to convince him otherwise. Besides, he's in love with my dog) He does have separation anxiety that we need to address.