My Belgian stallion is kept with a sterile mare. She keeps him in line. As he has never been extensively socialized because of his size I would not turn him loose with geldings or mares/babies due to the size difference. My Quarter stallions are rotated. At foaling they are kept together with geldings in a pasture out of sight of the mares and babies. If we are pasture breeding they along with the geldings are turned back in with the mares they will be breeding and run with bred mares and babies until foaling the next year. If for any other reason they are separated they are kept in a large pen (small arena size or portable round pen- 60ft) in the same field as their band. Depending on the reason I may put a companion with.