How do I trick my dad into doing a vasectomy?

RELATIONSHIPS    MARRIAGE   PARENTING

Dad loved and educated each one of us up to university and my mother's last born now 26 years graduated five years.

My parents were generally happily married until after their 30th anniversary when Dad went on a rampage.

He impregnated a 17-year-old in 2014 and the village leaders forced him to take her on as his second wife. That girl has had four children so far.

I advised Dad to do a vasectomy but he almost cursed me. He assured us that his young children are our responsibility claiming that he had spent a lot of money on us and our mother.

He is always demanding money for their school fees and other needs. He is so shameless that he even calls our spouses for money to take care of his young family.

This Christmas we discovered that he had impregnated a 19-year-old and taken her on as his third wife.

What can we do for our father, is he normal to do what he does at 72 years? Is there a way of doing a vasectomy without his knowledge?