whenever you hold your jizz inside of your dick by squeezing the head of your dick REALLY REALLY hard whenever you are about to cum. This will stop you from ejecting sperm. repeat process until you have a hardened ball of dry jizz built up in the shaft of your penis.
I've been saving this jizz pearl for the day that I run into Fred Phelps, then I will proceed to shoot it out of my dick like a cannonball into his head. Hopefully that will kill him.