The answer is: depends.
At my house, we have 7 intact females and 1 intact male. As long as none of the females are in season, or getting close to coming in season, we don't have a problem. That's mostly due to a lot of work nipping any leg-lifting in the bud very early.
Once a girl comes in season, all the rules can change. We never have both the boy and girl out together; when one is out, the other is always crated, they take turns in their crates. The girl always has the pants on when she is in the house, even if only for a minute. If she gets that scent on anything, the boy will be right there to mark. And the pants are still no guarantee that he won't smell her somewhere and mark. Ideally, we would send our boy off to "camp" when a girl is in season, but we don't, so we keep them separated and just put up with the occaisional marking. It's just part of being a breeder I guess.
If you have been breeding before, then I assume you were getting outside stud service. Perhaps that person can give you some further advice on dealing with a boy in the house with other females; nothing like a face-to-face conversation on the potential problems and solutions. Or, if you are showing, you may be able to get some advice from others after a show. You may be surprised how open other breeders are once they see you at shows and get to know you.