No dog breeding

[Natural Light Kid]

This is the opposite of the earlier thread "dog breeding". I just got a young female lab. I have never had a female, dog that is. I do not want puppies, but I don't want to have her fixed. I would like to leave that option open for down the road. I know nothing about them coming into heat. She will be exposed to males from time to time. What are some pointers to keep her from getting knocked up besides the obvious? Thanks.