What can you do to prevent a dog from getting pregnant?

No there is not, it is must easier to take a dog to get spayed. Humans have enough troulbe remering to take the pill themselves, than to try to remember to give their pet a Birth Control pill. It is much cheaper i nthe long run to soay, also will prolong her life and elimante the chance of a piometra which would need an emergency spay, and is quite pricey. There is a lot of info online with the benefits ofspaying.