My boyfriend's mom has two dogs Fronk (a standard poodle, about 5-6 years old) and Bailey (golden retriever mix, same age). They basically grew up together in this household, and up until recently have had a very loving, harmonious relationship. Bailey actually gets separation anxiety whenever Fronk leaves the house to go to the groomers or even just a walk around the block.

A couple weeks ago, we've noticed that Bailey is getting increasingly more aggressive with Fronk. Bailey will sit inside a bedroom doorway and growl at Fronk if he tries to come in the room. If Fronk is already in the room and he tries to get up on the bed, Bailey will growl at him then too. Sometimes Bailey will skip the growling and start barking and snapping at Fronk's face.

Meanwhile, Fronk seems to back down or get nervous when Bailey growls at him and won't let him in the room or on the bed. The only time Fronk does not back down is if Bailey skips the growling and goes straight to snapping and biting at his face (currently Fronk has a scratch under his eye from Bailey nipping at him a few days ago. A lot of the time when they are going to be put outside, Bailey will run for the backyard excited, but Fronk will try to run away and hide cause he doesn't want to be outside with Bailey.

Both dogs have been neutered, although I know that's not a cure-all. I just don't understand why this is suddenly happening and what we could possibly do to stop it.