Your female dog is due to come into heat in the near future, and you don't want it to breed. Decide whether you want to prevent it from mating in the short term, or whether you need a more permanent solution. If you're not planning to breed at all, make an appointment with your veterinarian to have your dog spayed before its season begins. If you want to breed later, however, your focus is on preventing your female from mating now.
Watch for the first signs of the start of your dog's season. Its vulva will swell up a few days before the bloody discharge starts. During this time, male dogs will be interested in your female but your female won't allow mating. Although a female usually only permits a male to mate with it after the eleventh day of the heat, it's safest to keep them apart from the time the discharge starts.
Diaper your female dog. Dog diapers are available from pet stores, or you can make your own using panty liners and squares of old towelling cut to size. This will prevent the male from being able to mate with your female and help keep your house from being soiled from the discharge.
Use the two-door method to separate your female from your male dog (assuming you have a male). Keep your female in one part of your house or apartment and your male dog in another; make sure there are always two closed doors between them. This will prevent any accidental contact that can lead in seconds to a mating.
Rotate the time your dogs spend in their crates. Keep the female in its crate for a couple of hours while the male is out, and then put the male in its crate while the female is out. As long as they're both never out of the crates at the same time, they won't be able to mate.
Speak with your veterinarian about an injection of Delvosterone. This injection can be given to your dog within 24 hours of the heat starting, and will suppress the heat for up to five months. The injection is reliable and has no lasting effects; your dog will resume normal seasons a few months after its last injection.
Keep your dog away from male dogs for at least a week after its discharge stops (whether this occurs at the end of the heat or as a result of an injection). Your female can ovulate from the fifth day to the twenty-third day, and sperm can live inside it for up to seven days after a mating, so your female is only safe from being impregnated once a full week has passed since the end of the season.