Dogs licking another dogs privarte area

[Maddogs2012]

I have 2 male dogs. Rick is a 6 year old Boston Terrier. Jeff is a 3 year old Bull-mastiff. They have been together since 2009. Over the last month or so, Rick has begun humping Jeff's head on a daily basis. In addition to the humping, Rick will lick Jeff's privates until Jeff gets a "pinkie", and at least once until Jeff "finished", for lack of a better word. We only know about the finishing part because my wife caught them just after it was done yesterday. Rick will sometimes try very aggressively to get to Jeff's private area and will actually push himself between Jeff's legs. Jeff is quite passive throughout. Whenever we have family members' dogs over, they will sometimes try to hump Jeff and try to get at his privates like Rick does. It's kinda disturbing. We'd like it to stop, but don't know how to explain it to the dogs. Again, this is relatively new behavior. Nothing in their daily routine or environment has changed. Any suggestions on how to get them to stop. Also, we have a female Min-Pin that pretty much stays out of it, and they tend to leave her alone. She's 4 years old.

[Margot49]

Is the female spay and the boys neutered?

[Maddogs2012]

Hello, I'm sorry that I forgot to add that. Both males are neutered and the female is spayed. Let me clarify also that when I say that Jeff "finished", his whole genitalia was out, like when dogs are "finished" breeding. I apologize for being graphic.