I've started to catch Paddington lifting his leg now too. He is exactly four months. He marked the steps leading to our patio, the wall next to his pee pad (repeatedly- what are these posts, Paulapoo???) and my dad's chair at the head of the dinner table...
I'm hoping it stops when we get him neutered. I'm going to talk to the vet about it when we go in on Saturday for his boosters.
-O