help again?

Seems like I only use this blog to ask for advice these days....

Dorian will be 3 in a few weeks. He is still adjusting to his baby brother who is now 8 months old. But it seems in the last month or so he has gotten very aggressive with Dexter. From the beginning, I think Dorian viewed little Dexter both as a threat and as a toy. And now that the baby is crawling and pulling up on things, Dorian is 1)even more threatened because the baby can get his toys, and 2)seeing Dexter as even more of a fun "plaything" because he can do more things now.

I know aggression between two close brothers is normal, but I am actually worried for the safety of the baby! Dorian does things like knock Dexter down when he has pulled himself up on the coffee table, or lie on top of him, or try to pick him up, or throw toys at him, or forcefully put things in his mouth. Dorian seems to get over-excited when he interacts with Dexter—he gets right in his face and screams, or pinches his cheeks, or buzzes his lips so that he spits all over Dexter.

I have talked to Dorian about how his little brother is not a toy, but a person with feelings and rights. We have talked about how he might feel if someone were to scream at him, or pinch him, or spit on him. I have tried to spend extra alone time with Dorian while the baby is sleeping. I have sent him to timeout 1000 times for hurting the baby. I have praised him for good interactions with the baby. What else can I try? I know he loves his baby brother, but he obviously doesn't feel like he has power over his world right now.