Get the 'kit', the one that has several dilator toys in graduated sizes.
Ammo-shell style anal dilators work well too.
the inflatable bulb goes in small then pumps to full diameter afterits inside you. They're the only thing I know of that mimics the real anatomy and physiology of a dog. For training, I can't say enough good things about Elypse art toys. virgin or inexperienced bitch was either in genuine pain or just overreacting and flailing about, but enough to be putting the breeding pair in danger of injury). Echoing that the cold water trick will likely work, it was an old breeder's technique if the tie needed to be broken in an emergency (ie.
