It is best to not do anything to get dogs unstuck after mating. It is a natural thing and trying to stop it may injure the dogs.
Dogs become stuck together after breeding. This occurs because the male's penis swells after ejaculation. The dogs may be stuck for up to 30 minutes. Throwing cold water on the dogs to separate them does nothing, and can cause the dogs to try to run away. The best thing to do is watch the animals and make sure they stay calm. Any sudden movement from the dogs may cause the male to bruise or injure his penis.