I have a son who is almost four, and sometimes is reluctant to stop what he's doing to go potty (because he doesn't HAVE to go). We try to make it a non-issue by saying, "Just get the extra potty out." I also work as a director in a child care center, and when I sub in the preschool room, we have some of the same issues with children who say they don't have to go potty. It is helpful to have a routine there, as I say something like, "That's okay, but we always head to the potty before we go outside/after nap,etc. You don't want to wait until it's a potty emergency." You might try to build some things into your day that require a potty break before going, and then just be matter-of-fact about it. Try not to tie it to the ending of the activity he enjoys. You could let him know that you'll be heading to the park/store/library, stop the activity, then have him head to the potty. We used to tell our daughter that the bathroom was the last stop before leaving the house, and it just got to be routine. Good luck!