My gut tells me that Rocky is just being exposed to more things being that it is Spring time and people are out and about more (and yard statues are more mobile, while they probably stayed in the same place all winter
When Aidan would bark at things like this I used to think that he was being protective of the house, but after his ATTS temperament test and comparing his behavior to Brutus, I really think these things just scare him and he is trying to get them to go away. His bark sounds menacing, but it is more of a fearful bark than anything. He needs more socialization, and I think once he realizes these things are not a threat, he will bark less. One thing I have noticed is that the hair stands up on his back when he is uncomfortable, so he is not just warning me of something being outside, he is scared.
Brutus's reaction is very different. He just stares at things outside the house with his tail straight up, very alert. He does not bark unless the thing in question approaches the house. Then he lets out the evilest bark I have ever heard, and he runs over to bark at me as well. This is more of a protective reaction and he trying to 'warn' me.
When Rocky barks at these things (wagon, guy in the driveway, etc), does he bark while backing away? Or does he approach the thing while barking? The first one is more of a fearful and defensive reaction to something he has never seen before, while the second is more of a protective bark.
And if he is being protective, then maybe he is just now seeing the house and the backyard as 'his'.
How long have you had Rocky?