Play Fightinig?

Question
I have two dogs, a boxer and a doberman. The boxer is 2 now and we've had him for a year and a bit. The doberman is slightly younger and we just got her about a month ago. The doberman has many many bad habits which we're left to get worse and worse by her previous owners, however we are making some head way. My biggest concern, one i just don't know enough about is the relationship between the two. I have had dogs all my life but never this type of "working" breed and i can't seem to justify the way they, so my boyfriend says, they "play." There is an awful lot of growling from the male boxer, but never hair or teeth. The female is not vocal at all when playing, but i don't know if she is able to control herself. For the first couple of weeks they were doing a lot of mounting each other, and jumping up and boxing. Now however they seem to play by grabbing each others necks as they lazily lie on the couch. One will get on top the other and hold on and then switch. The male is nice about it and is just nipping, but the doberman uses her whole mouth and really grabs tight, so tight that my boxers neck is very red with bumps. Is this playing, when should i worry?

Answer
Sounds like it might be a dominance thing,and often once they sort it out,it will stop on it's own.And what you can do is muzzle both dogs,so they can sort it out,without hurting each other-this doesn't sound overly serious at this point,but the muzzle thing might prevent any injury