I have 6 cats. 4 females and 2 males. 1 of my male cats, has recently become aggressive toward the other cats lately. I've seen him spray on our back porch, but not in the house. The porch is screened, so they don't go outside. He was neutered when he was a kitten, before I got him. He's around 3 or 4 years old, I believe. He has never been aggressive or pushy with the other cats until recently. All of my cats are spayed/neutered rescues. Any ideas?