My sons little guy started that at a very young age(probably around 12-14 weeks), they got him neutered at 5 1/2 mos and he still lifts his leg in the house. He's not marking, he's downright peeing. They even bought him one of those little fire hydrants and put it in the middle of his pee pad. He likes coming to Grandmas house, but, when he leaves I have to start cleaning, although, luckily, he holds his bladder for quite awhile |