It is very easy to become frustrated when litter training, but i think the key is repetiton and consistency!

Have you tried restricting his play area? Maybe an exercise pen connected to his cage, that way you can cover the floor with a blanket and put a litterbox in the play area and his cage?

For the flipping of his litterbox, if his cage allows drill two holes near the top of the litterbox and affix it to the cage using zipties, or use duct tape? Be creative! My boy used to move his around and make a mess but finally figured out it wasnt a toy when it wouldnt budge.

Its going to take some time and patience to create a good litter habit. As much as it sucks, pick up any poos, soak pee with tissue and put it in his litterbox.

Another thing that works for my bunny, is praise. If you find him in his litter box pooping or peeing, even eating hay to begin with! Praise him and give him a small treat. You could also try clicker training!
Im still trying to get my bun to associate a clicker with reward for good behavior.

Three years old is not too old for neuter surgery. It usually is difficult to fully litter train a rabbit who hasn’t been spayed or neutered.

I agree that restricting his area with an x-pen would also be a good idea, to keep him in close proximity to the litter box, and to make cleaning easier since the poops wouldn’t be as scattered.

He’s probably marking his territory – It’s only been two weeks.

One thing that helped me litter train Julie (who still leaves the odd poop outside her box) was baking soda. I would move her to a travel cage, then sprinkle a bit of baking soda anywhere the litter box wasnt. I would let it sit for a few minutes, then vacuum it up. Then I would use the age old water-vinegar solution to wipe down the other parts of her pen. I think the baking soda neutralized the smells until she realized that only her litter box smelled like a place to potty, lol.

Is he using his litter box when he is caged? Or waiting until he comes out and doing most of his business then?

Do you know much about how he was housed previously?

I do agree about restricting his out-of-cage space while training. Too much space can be a set-back.

When you’re free, it’s good to just monitor that rabbit bottom like a hawk — immediate intervention for poops/pees outside the litterbox is a really effective way to drive the message home.

Another litterbox (or two) could be in order when your rabbit is okay to free roam, after learning the litter box ropes. Wick started with training in the pen, then was given free-roam space. I soon realized it’s asking a bit much to run from the bedroom all the way back to the pen in the living room when he needs to poop/pee, so he has two additional litterboxes in the free-roam space. For training, when he would poo/pee outside the boxes, I pick him up immediately and bring him to the closest of the three litter boxes, that way he got the message that he should travel to them.