My little 5 month old Lionhead, Elliott , has recently taken to leaving a few pellets in my bed every morning.  He is semi-potty trained in that (before this latest development) only pooped and peed in his cage.  He can run free upstairs for the most part and only uses his cage to eat, drink, and go to the bathroom.  He has an actual litter box IN the cage, but NEVER uses it.  I was fine with this scenario since he always kept it in the cage. 

But, the other day I accidentally closed his cage over night.  That morning I woke up to poop in my bed.  Now, he's done it every other night since then - even though his cage is open.  He still uses his cage and only leaves a couple pellets every night.  He never does it during the day so I can never catch him. 

I like it that he can run free at night and hop in bed if he feels like it and I don't want to keep him penned up.  What can I do to break this new habit?  And, why is he doing it anyways?

Hmm, well he probably either thinks A) the bed is a potty, or B) he wants to claim the bed as his own, both of which are kind of cute actually...but I guess I'm not the one with pellets in my bed!! Since its just a few I would assume its the territorial thing, but I am not so sure how one goes about fixing that...maybe prevent him from being able to get on the bed for just a few nights so you "reclaim" your territory? Is he neutered? Maybe that would help calm his territorial instincts?

Get him neutered if he isn't already

He's not neutered and the vet that I always go to thought it was ridiculous when I asked him about getting him neutered.  I wanted to get him a friend, but then decided against it and the vet said that there was no reason to fix him then...

Could he be acting out because he's lonely?  Does he really need to be neutered?  He's started doing it during the day now too.  : (

No, around the 5mo. time bunnies are in adolescence. Compare it to the terrible teens humans go through, where they start acting crazy because of the hormone changes. If your vet is not recommending neuters, this vet is definitely not a rabbit savvy vet and should not be practicing on rabbits. You can find a list of rabbit savvy vets here: http://www.rabbit.org/vets/index.html. If you are located in CA, there are alot of us on here who can give you vet recommendations as well. You will definitely want to take him to one of these vets from now on and ONLY get the neuter performed by one on this list.

Btw, he looks sooo cute (your avatar pic)!

Once he is neutered, then you can consider getting him another neutered friend.

Welcome fallbrookkate!!  I agree with Poopy!  Your vet is not rabbit savvy, and I would seek out another vet asap.  His comments are ridiculous.   Do you live in the U.S.?