Sudden aggressiveness towards other dogs

[Shepherd2012]

Hi there, hoping you can help me.

I have two 16 month old german shepherds - one male, one femail and they're littermates.

We socialised them really well when they were pups and they're great with other people and kids and until recently, have always got a long great with other dogs.

They're pretty well trained and usually very obedient.

We have a local park and there are a group of regulars of an afternoon and the owners all stand around and chat while the dogs play
with each other. Loads of different dogs and different breeds. It's always been fun.

The last couple of times however my husband has taken them up there one of them has picked a fight with another dog and even though none of the dogs were hurt, it was pretty ugly.

Everyone was suprised because our dogs have a reputation for being so friendly.

We thought it might have just been a one off but the last couple of times the female has just launched at a friendly labby for no reason. The labby was wagging its tail but our girl just reacted.

We're very confused. Can anyone shed any light on why this might be happening and offer any advice?

Any help would be much appreciated.

[KZoppa]

Shepherds are not generally dog park dogs. They tend to have a more dominant personality than most other breeds. Without having been there to see exactly what happened, I'm not even going to try to figure out what yours girls motive was for launching at the lab. Female shepherds, in my experience, don't usually care too much for other female dogs. My older female is a very dominant girl and has moments where she simply does not even like my younger female. My younger female is almost 3 and adores everyone. If I don't manage interactions between Zena and Shasta, Zena will let everyone know she's not happy with something. But then I bust Zena cuddled up next to Shasta while Shasta is crated or they snuggle in the hallway when I'm drying my hair. Beyond that, interactions between the two are limited and supervised. Zena was fine at the dog park when I took her but if my husband tried to take her, there were fights.

[Dotty]

I have littermates the same age as yours, both female. They are great girls, we train, train, train. No matter what though, they can not be taken out together, if one dislikes another dog, it becomes a pack attack.
My husband walks one and I walk the other.

From my experience and I am far from an expert, I would avoid that situation where the one had an outburst as it is a rehearsal for future behaviors.