Why do dogs lock when mating and how long is a dog's penis?

the males pepe swells up to get stuck into the females vajaj to make sure sperm get in to breed or to have babies
Its normal...looks odd but its the way the male insures that he is releasing all the sperm and not letting any go to waste. The male just gets swollen and she tightens, so it will soon release, never try to pull them apart!!!!!!!