[Critter]

I have two little boys, love them both so much. One of them, Harley, loves to mark when we are outside. He never does it when we are in the house, which doesn't seem to be the problem. The problem is when we go out to other places or when other people come over to the house and they have something that smells of other dogs. He will try to mark them or their property. It is so embarrassing. Recently I noticed when I go to my parents home (who has a dog) when we walk into their home he will walk in and start marking their home. Is there anything I can do to stop this. It seems to be getting worse. He is 3 years old and is fixed (we did it young, can't remember when but it was as soon as they recommended) and he didn't start out this way, its only been over the last year he started doing this and its getting worse.