Lurker here, not sure if this has already been addressed so I apologize in advance if it's been posted elsewhere...

I recently adopted a eight-year-old spayed chihuahua mix. I have another dog, a four-year-old spayed chihuahua mix that I've had since her birth. The dogs thus far get along well, enjoy playing, running, etc. They have no issues sharing food and don't seem territorial with their toys or even bedding. They however have always had their own individual crates, beds, and bowls. 

Recently, though, the older dog started mounting the younger one. I'm not sure why. The mounting results in snapping, though she doesn't stop the mounting unless I physically remove her. The dogs get along fine otherwise, but I would like for the older dog to stop mounting since my verbal cues (firm "NO!") don't help.
user
Old dog mounting younger dog, not sure if it's a problem and if I should
assistant
Lurker here, not sure if this has already been addressed so I apologize in advance if it's been posted elsewhere...

I recently adopted a eight-year-old spayed chihuahua mix. I have another dog, a four-year-old spayed chihuahua mix that I've had since her birth. The dogs thus far get along well, enjoy playing, running, etc. They have no issues sharing food and don't seem territorial with their toys or even bedding. They however have always had their own individual crates, beds, and bowls. 

Recently, though, the older dog started mounting the younger one. I'm not sure why. The mounting results in snapping, though she doesn't stop the mounting unless I physically remove her. The dogs get along fine otherwise, but I would like for the older dog to stop mounting since my verbal cues (firm "NO!") don't help.
user
Older dog mounting my younger dog. No actions of physical removal. No verbal instructions of
assistant