Usually, it will slightly but definately not as much as the first time, because the hymen (in girls) is usually already broken. Unless you have sex every single day, the vagina opening usually shrinks slightly (I doubt to the original size), so when the penis enters it again, it stretches out again. But it won't … Read more
If you're 100% sure that you're infertile and your gf is infertile THEN DEFINATELY!
Determining the sex of any dog is very simple, you simply see if they have a penis or a vagina.
And they have six nipples, though all dogs should have that.