Hard to answer with the limited info you give. Was he ever potty trained to begin with? Is he continent of his stool? Is this a new thing? If he is 4yrs old and this is an on-going issue, then I would begin at the Pediatrician's office and see what tests can be done there before I'd do anything else. Some kids have smaller bladders or other bladder issues and only a medical doctor can diagnose those. Best of luck.
Does he wet the bed if so that is pretty normal for a 4 year old male.
Does he go all the way in his pants or just a little. We need more info.