Yorkie thinks she's a rottie

Can anyone help, my yorkshire terrier keeps attacking our rottie. I dont want to come home oneday and see my yorkies legs going down his throat.

Sadly we had to rehome the yorkie last night.

We need more information on when and why these 'attacks' occur. What does the Rottie do when they happen? How do they start, how do they finish?

If there is a chance that they will hurt each other then never leave them together unsupervised. Make sure that they are in separate rooms, or that one or both are crated, when you are out.

I agree with SB

She just starts on him for no reason, he can just sniff her and she will go for him. Its not just him she goes for the others to. If one of them cries she just jumps on them like a wild dog, she will do it infront of us and i will shout at her and eventually she will stop.

How old is the Yorkie?
How long have you had her?
Has she always done this, or is it a recent development?
How old is the Rottie?
How does the Rottie react?
How do the other dogs react?
Do you think these 'attacks' are real, or might it be play?
Are you sure there is no resource guarding involved? E.g. possession of toys, food, your attention, etc.
Has she had training?

The usual course of action would be to let the dogs sort it out for themselves but, given the difference in sizes, you need to be careful. If you don't teach her that her behaviour is inappropriate then, sooner or later, one of the other dogs will teach her. This could have unfortunate results for the Yorkie as even a warning nip or a swat from a paw could cause damage.

Probably the best way would to remove her from the room immediately she starts. Let her back after a minute. If she does it again, remove. Shouting at her is obviously not effective and the shouting may also be inadvertently 'punishing' the other dog who may not realise that you are yelling at the Yorkie and not at him. Keep putting her out until she associates cause and effect. Praise her for any quiet and gentle interaction with the other dogs.

Do not leave her unsupervised with the others.