Male/Male Dog Aggression

[mariacynthia]

My 4yr old male dog is attacking my 9 year old male.

We also have a 1 yr old female which neither have aggression towards.

Moments 4 yr old has attacked 9 year old;

1. When there is someone who comes to the door, 9 yr old goes to the door and barks. 4 yr old jumps on 9 yr old biting.
2. 9yr old playing in yard with big tree branch. 4 yr old playing different area of yard. Runs up and attacks.
3. I was sitting on couch with 9 yr old. 4 yr old gets up, walks over to side of couch where we are, stiffens up, and tries biting him.

My 9 year old after attacked starts to fight back, but he is old and it isn’t fair. If I tell them down, the 9 year old listens but not the 4 year old. He keeps going and I have to physically remove him. I’ve been bitten many times doing this.

We keep them separate erate 75% of the time because of this but we try to integrate them and fix the behavior with keeping them occupied on different things, exercise, etc.

It’s just not working out and I’m worried we will need to rehome the 4 year old. Does anyone have advice?