I have a big female Newfie mix rescue - about 4.
She developed (or it was lying dormant) aggression with certain new dogs she meets.
Whether at the dog park or on a walk, she has to get up in their face and dominate them.
As you can imagine, some dogs don't like that.
And there can be tension...
I'm fostering a Newfie mix female - about 4 years old - 100 pounds.
She has a dominance/aggression problem.
Basically, for any new dog (mid to large size) that comes to the park, she has to run up to them and get in their face.
As you can imagine, it can trigger a fight once in a while.