I have a mutt named Riley who is a mix of shih tzu, bichon and poodle. He's male. He's fixed and has been since 6 months. If I get a second dog do I have to worry about marking in the house? Riley does mark on our walks but he's never done it in our house. However, he did do it at my sister-in-laws before I could stop him (she has a male dog). Should I get a female instead?