You can have a vasectomy or a condom. It seems weird to me that if not having children without your knowledge is so important to you, that you expect women to be the ones taking care of contraconception. And that you do not explicitly tell them.

Not that it is ok to not tell, but I think that the easiest solutions would be that you take responsability about contraconception and only stop using it with a woman you want to have children with.

I mean, if you have been using condoms, is highly unlikely that you have an unknown biological child. You use condoms on one night stands, right?

Plus, most women who want to become single mothers use artificial insemination. That way, if they don't want a father around, they make sure of it. Since the sperm for artificial insemination is from men who have forfeit their right as parents of those childs.