I used to keep my rabbit in a cage with corrugated plastic flooring and a corner litter pan with wired flooring. No matter how hard I tried to train him, he'd only pee on the floor and I'd wake up every morning to clean the white plastic floor turned yellow from all the peeing. He didn't even pick a corner, it was basically anywhere that seemed good to go.
I got rid of the cage completely because I was just tired of cleaning it up and bought 3 small sized cat litter pans, filled them up with CAREFRESH, a bowl for pellets, and some hay and VIOLA. It really did the trick. I placed the boxes in areas he used to like to pee around the living room put some of his poops in there, and it was like magic.
Now he's cage free and uses his litterbox very consistently. I've had this set up for about 1 week now and he's only had a booboo once. I still wake up a little scared to see what the living room floor will look in the like in the morning but I'm always glad to see he hasn't made a mess! He still leaves some marbles here and there, but mostly right around the boxes and at this one spot he likes to lay and groom himself.
If you don't have the luxury of cage-freeing your rabbit, I suggest that you make the cage floor a completely different consistency than the litterbox. Also, I've noticed rabbits like to pee in areas that seem plush and fluffy (like carpets, beds, linens....carefresh!!!). Entice your rabbit into the litterbox by placing your food bowls in them and also make sure that the walls of the litterbox are high enough so that the rabbit HAS to go in the box to eat and drink. That way he'll stay in longer and will hopefully do most of his bathroom business in there while eating.
Hope this helped!
But seriously, I was really about to give up on my rabbit because he just peed everywhere and would then sit in his pee and lay down in his pee and spray his pee. It was so frustrating having to deal with that and all the biting. Now that the peeing situation is gone, the biting seems a lot less..harder to deal with. He also seems much more happier and started doing binkys now that he doesn't live in a cage most of the day!