Remind him you could still get pregnant if he perforates the barrier between rectum and vagina! And that anal does not prevent STIs.

Tell him you'd rather use abstinence if that's the case.

Tell him, that you will give him anal first.

Tell him that’s where poop comes out.

Tell him that what he gets to do to you, you get to do to him.

He's not wrong though...

100% effective.

So you get a massive strap on and ask him to bend over.

I don't see the problem, some women prefer it. Also you avoid the stress of wondering if your birth control was effective or not.

He took his shot, regardless of the outcome, and he didn't go ahead and do it without your permission, which makes him better than quite a few other people who have been mentioned on this site.