In addition to what was mentioned above.
If the litterbox isn't to your rabbit's preferences (too small, far away, full etc) they will definetly let you know.
My rabbit, Storm, he would rarely wee on my bed. He only rage-peed when his litterbox was left uncleaned for a single moment longer than he thought was appropriate. Since he'd be unwilling to use the dirty loo, rather than doing it on the side, he came to me before pointedly going to my bed and taking a leak.
It's also true that neutering helps but won't always fix the issue after that. My first boy, Musti, he just liked digging on my bed and out of pleasure often left puddles for us to clean. Even after neutering, he kept doing it, though luckily not as often. One time, however, he did confuse my bed/wall gap for his toilet and let loose on the curtains.

he looked so confused when i picked him away and grumbled about having to rearrange half the room so i could clean the wall and under-bed.
I just learned to live with the fact that i needed to change my sheets at least twice a week.
I'd reckon you'll find a way to block your bed from him or invest in a few pairs of waterproof bedsheets.