I agree that a vet visit with full senior blood panel and urinalysis would be a good idea at this point.
Originally Posted by davmar77
the second box is smaller and shorter so we thought that would help but it really hasn't.
Winston's idea of trying a different litter box is good. Find a very large, flat, under-the-bed style storage box, perhaps even trimming down one of the sides if necessary. It's pretty much a guarrantee that your kitty has some degree of arthritis (80-90% of cats over the age of 12 do) and it's quite possibly painful for him to get in and out of the box. The smaller the box, the harder it is for arthritic cats to turn around in, and the ones with high sides are tough to get in and out of.
Not sure what type of litter you use (any changes in that department?) but you could try some Dr. Elsey's Cat Attract, which has some added herbs that cat's find irresistable to pee on.