My 15 month old keeps removing his diaper?

we have tried everything from putting on backwards and pants w belts and bibs forwards and backwards heck tried plastic diaper and onies over diaper this child is like Houdini I don't believe he is ready for potty training he seems to be a lil adhd and cant sit for more then a 3 sec span but if he had his way he would be a nudist my baby sitters are at there wits end too nothing like cleaning poop off the carpet grrrr