I have two 7 month old toy poodles, they are brother and sister and I have had them since they were 8 weeks old. The problem is with the male, he attacks his sister on a daily basis, it's not play fighting, it's a vicious attack. Both of them were desexed at 5 months and that is basically when he started doing it. Today I put their leads on to take them for a walk and between doing that and putting in my shoes, getting my keys etc, he had attacked her 3 times! He will also attack her when they are sitting on their mats in the kitchen with us, he will randomly just start growling at her and then attack. He also attacks her when my parents come to visit. The rest of the time they play well together and she recovers from the attack pretty quickly (she fights back to protect herself and has never been seriously hurt). But this can't go on, I think I will need to re-house one of them but would like to do whatever I can to try to solve the problem first. But I don't know where to begin!

Siblings often don't live well together because of the need for one to dominate. You will either have to spend a lot of time training, or find a new home for one. Start with a short leash on the male when you know the situation is likely to result in an attack (food and attention). Get a book on training, and prepare for the fact that he may not be fully trainable. But some siblings do work out an arrangement of more friendly dominance, so it's worth a shot, IF you are willing to do the work.

It usually has nothing to do with being siblings, it's a pure dominance thing, and poodles (as are many other dogs) are prone to it. Sometimes there is nothing you can do but separate. I have dogs who need to be separated at all times, it's a way of life. You can try things such as obedience classes which will help establish you as alpha and stop the male from feeling the need to assert dominance. Also when your dog is looking to you for commands, they don't have the need to look for a job (in his eyes he thinks he is protecting you or his "home"), when you give him a command, he now has a job to do.

Some dogs just have inter-breed aggression while other dogs don't. You can never tell and some dogs it's something they are born with. There usually is no magic cure, only ways to avoid and control.

Even though it sounds bad with the barking and growling, typically it's more scare tactic unless you are needing to get stitches. Lets face it if he wanted to do damage he would. That's their way of communicating, so it always sounds worse than it is. Not saying it's something you should ignore, definitely not the case as this will only get worse.

I crate one dog on one side of the house and switch their free times up. Some days they get along fantastically, you can probably already tell the difference in body language and probably can almost predict a fight. This is when you need to intervene and separate.