Dogs don't have periods, they go into heat (Estrus)! Normally it's every 6 months! They are in heat for 3 weeks! Keep the female away from males that are Not Neutered for at least 3 1/2 weeks to be safe! When she goes outside to go potty, someone needs to go with her and bring her back inside when she's done. Do not ever leave your female outside or near an Un-Neutered Male, while she's in heat! If you get your female Spayed, you won't have to worry about her going into heat or getting pregnant!