Two Dogs getting along

Question
I have a yellow lab that we got from pound a year ago approx. age 4 yrs.She is great except with other dogs.My wife grandfather passed and we inherited his mixed dog.Approx age 4 yrs. We are trying to get them to get along.Both are fixed, females.We had them meet in neutral area, walked them together etc, but the lab wants to hump the mix and the aggression begins.Any ideas?

Answer
What I have found that works best to muzzle both dogs,then they can sort out there ranks without hurting each other. Then once thats sorted,then the fighting will stop. The yellow lab would most likely be in charge-and once the other dog knows this they won't need to fight it out