Their inquisitive nature may see them make an effort to trespass around spots where you have restricted access to. Where cat behaviour is deemed to be unacceptable, steps can be taken to nurture and reshape attention and behaviour to desired responses.
While litter training varies between each unique cat, there may be times where difficulties arise. A change in litter visits indicates something that is amiss. Inspection of the litter tray and surrounding area is important. Cats maintain an expected level of sanity and if not met, they will simply refuse to use the litter box. This is not a behaviour to be corrected, rather an indication that action needs to be taken to remedy their place of litter.