Every time I've gotten pregnant I never worried about just laying there and trying to keep them in. DH is one of those guys who, I swear, tries to thrust to China when he ejaculates so everything is usually right up against my cervix anyway. I'm NOT a fan of tempting UTI's and usually have to pee right after an O so I'll happily do a pre-emptive clean up with tissues and then waddle my happyself to the potty, do my business, and finish cleaning up. I can't stand the feel of a mess.
Sperm ARE strong swimmers. They're excellent at combating gravity.