I chose "physical alteration," not because I've been snipped yet, but because I will be when the wife and I are done having children.  Before we were married, we used condoms.  After, using nothing, it took us almost a year to conceive our first.  Now, she breastfeeds our 3-month old daughter as her sole source nutrition, which has been shown, if done regularly, to have a contraceptive effect, but honestly, we're not counting on it...we actually want to have our 2nd (and final) ASAP to get the house out of diapers 

.  Once we deliver our second, I'll get a vasectomy.  There's no convincing reason I've heard of not to.