What do I do in a serious situation with a very aggressive dog?

We have a dog named Magnus that we've had since he was a puppy. We have never abused him or doen anything bad to him. He has always been "growly" but never seemed too threatening. He always seems like an anxious animal. I didn't like it but spraying him with a water bottle wasn't working so we... show more We have a dog named Magnus that we've had since he was a puppy. We have never abused him or doen anything bad to him. He has always been "growly" but never seemed too threatening. He always seems like an anxious animal. I didn't like it but spraying him with a water bottle wasn't working so we hoped he would grow out of it. (He also isn't nuetered. I keep saying we should do this but my brother says its too expensive to bother.)

I sat down on the couch a couple of days ago and started petting him. He startled growling while slowly pushing his head into my lap (thought he was playing with me for a second there) and then he crawled up on top of me, putting his paws around both my sides. He pushed his body hard down on my chest and wouldn't let me get up all while growling at me. He then put his mouth to my neck, slighlty opened, and held stock stil and growled while keeping his tail straight up. He nudged my neck a few times. We stayed there like that because I felt if I pushed him off, he would have sank his teeth into my neck.

And now he jsut bullied me out of the fornt living room. He jumped off the couch as I was putting my other dog outside and pushed his head against my leg and started growling again. He followed me this way all the way until I was out the room and then my sister came in and he ran off.
We raised this dog since eh was a puppy. He's been growly for months now but nothing this extreme? I'm scared he's gonna attack me one day.
Update: (A lot of you people in the comments are being insanely rude. You have no reason to call me stupid or idiotic.) So to answer a few questions, this dog isNOT mine and I have not been responsible for his training. I simply live with these people. This is my brother's dog and putting him down is strictly out of... show more (A lot of you people in the comments are being insanely rude. You have no reason to call me stupid or idiotic.) So to answer a few questions, this dog isNOT mine and I have not been responsible for his training. I simply live with these people. This is my brother's dog and putting him down is strictly out of the question here. (My brothern or my parents would ever allwo that and I don't have a single say in it)
Update 2: I am 22 year old female, 5'3" tall and NO I was not on my period. My dog's owner is away on vacation atm and I will tell him about it as soon as he comes back. I have NEVER with all the dogs we've ever had in this household, EVER had a problem with asingle one of them. This is completely new... show more I am 22 year old female, 5'3" tall and NO I was not on my period. My dog's owner is away on vacation atm and I will tell him about it as soon as he comes back. I have NEVER with all the dogs we've ever had in this household, EVER had a problem with asingle one of them. This is completely new territory for me. I do not have a say in the matter of this dog but I need to knwo what I should try to do. Should we take him to the vet when being neutered to talk about behaviour issues?
Update 3: I have talked to my family and am trying enforce soem info I found on the internet. I'm taking away the couch he's protecting and took away all the sticks. I'm watching my father like a hawk to make sure he doesn't feed him any table scraps. He challenges everyone by growling at them and so I told... show more I have talked to my family and am trying enforce soem info I found on the internet. I'm taking away the couch he's protecting and took away all the sticks. I'm watching my father like a hawk to make sure he doesn't feed him any table scraps. He challenges everyone by growling at them and so I told my family to not yell at him nor pet him. Simply stand your ground and stare at hime until he backs down. And Magnus DOES back down.
Update 4: He usually goes under the bed or chair. Your first option is NEVER to put a dog down immeditaley, especially since he has not bitten a single person OR animal. Whenever a dog shows unusual behaviour, people's first reaction is "KILL IT." Obviously you have to put time and effort in on the animal you... show more He usually goes under the bed or chair. Your first option is NEVER to put a dog down immeditaley, especially since he has not bitten a single person OR animal. Whenever a dog shows unusual behaviour, people's first reaction is "KILL IT." Obviously you have to put time and effort in on the animal you decided to raise. We'll figure this out.
Update 5: Until I feel until we have a better hold on him, I won't get lower than him or sit down next to him until he knows I and everyone in the house OWNS him, not the other way around. My brother, who's the owner of this dog, has horribly trained him and I had no say in this. So I WILL be taking action. When I... show more Until I feel until we have a better hold on him, I won't get lower than him or sit down next to him until he knows I and everyone in the house OWNS him, not the other way around. My brother, who's the owner of this dog, has horribly trained him and I had no say in this. So I WILL be taking action. When I walked him, I kept him within five feet of me and I didn't let him lead ME around. I made him come to ME for food and when I walking him, and I waited until he did. I'm stubborn. I'll win.
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