First: supervise and see what he gets into; You may think you are fully bunny proofed and then they will show you different!!!
Check and double check your bunny proofing. Look at the section on this website on bunny proofing its fabulous!
Second: Use hay as your primary litter (maybe stick some other type of litter under for better absorption-a bunny litter though) so that pancake wants to be in his litter box. This is working well on my hard to litter train bunny!!
Always make sure you’ve really cleaned any accident’s up. The smell will make them want to go there again. Vinegar will get rid of the smell, spray on carpet after you’ve cleaned pee up. Clean up poops frequently to keep poops from encouraging more poops.
Check out the section on litter training on this site, it’s also fab! More litter boxes=better!
Triple-check your bunny proofing! Make sure you don’t leave clothes or valubles out, they can become bunny toys in a split second!