Rabbits mark furniture that smells like their humans (beds, sofas). There’s not really any magical way to stop it. It usually does result in the rabbit just not being permitted up there. Some people have tried covering the bed or couch with a shower curtain and allowing the bun to mark it to his heart’s content for a couple days, and sometimes they’ll stop after they think it’s fully “theirs”, but… unfortunately, that does not always work.

My 3 yr old dwarf mix, BunBun, does the same thing! He LOVES to come into the bedroom (usually we keep the door closed cuz it’s not bunny-proofed) and he hops up on the bed with us. He plays and digs at the blankets and sits there getting petted like a little king and then… he pees >.< . When he had his bladder sludge, I used to have my hubby hold him and I was give him sub-Q fluids on the bed, then we would let him play. So we thought maybe it was due to the stress of getting the fluids, but he still does it now that he's off the sub-Q's and just comes in to hang out. Like Beka said, it's their way of marking things as theirs- I think they pee on furniture that they especially like and find extra comfy, like beds and couches. Of course it has to be someplace where the pee can really sink in and make a nice stink .
BunBun used to pee on the couch too (we had to get a new one). He had a habit of ripping the stuffing out of the cushions and literally digging/biting his way INTO the couch. Therefore, he was frequently removed, which made him very angry. So I think the peeing there was an act of revenge. There’s not much you can reallly do with Stan besides take him off of the bed, but I don’t know if that will teach him anything or just hurt his little feelings. We just put a few thick towels down when BunBun visits the bed now. Good luck !

Velvateen did this too. Try letting him up in small increments- 5 minutes to start, maybe less. Every 5 minutes, take him off the bed and put him in the litter box. When he goes potty, give him lots of praise and put him back on the bed. I’m not sure if this would totally work for you because when Velvateen did it, he was a baby and I couldn’t decide if he was marking or just had no bladder control. Maybe something to try though!
Is Stan neutered?

I really ditto Tate’s suggestions-rather then correct or take away the priveledge-just don’t let Stan fail (i.e. put him in his box before he potties on the bed)

Also-maybe try giving Stan his own blanky he *can* dig and pee on-OR a diggy box (Box filled with shredded paper)-if he has an outlet for digging he might let his dig-potty-onthebed habit go quicker

I’m curious, are you finding Stan is doing this more in the morning then evening or vice versa?