Some sort of zinc-blocking implant/pill might work.
Men with zinc deficiencies tend to have low fertility. This is because bollocks are zincy and fannies aren't, so when sperms are in a low-zinc environment they swim like mad because they think they're in a fanny. If a man doesn't have zincy bollocks the sperm go into omg-we're-in-a-fanny-find-the-egg mode and tire themselves out and die.
( Bob Todd whee, Fri 28 May 2010, 15:02, 3 replies)

*sniff* Poor little blighters.
(An Alien sneezed on Bill Oddies binoculars, Fri 28 May 2010, 15:19, closed)

Please tell me you teach sex ed

(Sivvus trolley collision in the fruit aisle led to a jam, Fri 28 May 2010, 16:21, closed)

Don't we need zinc for other things though?

(Falstaff's Spiritual Successor, Fri 28 May 2010, 17:55, closed)