No side-effects, no movement in the food chain, safe for pregnant creatures
Porcine Zona Pellucida Vaccine:Why in the heck don't we (as humans) have this option? Yes, it wouldn't work for immunocompromised persons, and 90% is not incredibly excellent. Look at diaphragms, though. Success rates between 83% and 94%. Condoms are between 85% and 98% and withdrawl is between 72% and 96%.