Secondary Mentor

I think secondary mentor role is basically to help student and the first mentor in the area that second mentor is needed. For example I said I am looking to do some Architected 3D modeling so first mentor would be Albert or Clint that are expert on 3D and then secondary mentor can be somebody from engineering school with more knowledge about Architect than 3D. I think it won't be very good if both mentor that we choose are expert in one area, like both are expert in 3D so then there is no point of having secondary mentor to me, meanwhile it can cause some not wanted conflict between all three too. I exactly have no name for secondary mentor but if I choose to have one I will go with some one from engineering department or somebody from industry.