[Marss]

Hello! So Flint loves marking. He is marking everything in the backyard and is also marking over where my other dog pees as well.
He is grass pad trained inside and goes outside as well. He is preferring outside, which is great.
The issue is that I found a marked area at the corner of one of the dog beds in the house.
Any hints on helping to make sure this doesn't get worse inside the house?
I watch him but I think he did it when I was showering. (Hubby was in living room with him)