My son called me just last week with the with the same problem with my grandson. I did a bit of research and found the following in a book called What to Expect from your Toddler. I realize a 4 year-old isn't a toddler, but the suggestions still apply. Please forgive any typing errors. Hope this helps.
"Accidents are an inevitable part of learning the the potty---just as falls are an inevitable part o learning to walk. But whether they're occasional or frequent, sincerely accidental or accidentally-on -purpose, the less said about them, the better. Lecturing Threatening, or otherwise making a fuss will only promote resistance in a rebellious toddler and diminish confidence in in a reticent one. Punishment is certainly not warranted; just as you would never have thought of punishing your toddler for falling when learning how to walk, neither should you consider punishing your child when learning to control his bladder. Don'[t demand an apology (it was and accident, remember) or a confession ( unless there's a renegade puppy on the premises, there will be no doubt who did it).
React to an accident as casually as you possibly can. If your child seems upset, be reassuring, "That's okay--you had an accident. Not problem. Maybe next time you'll get to the potty in time." Change his clothes without negative comment and without delay (forcing your child to stay in wet underpants in order to teach "a lesson" is cruel, and will humiliate and /or anger, not motivate). To foster a feeling of self-sufficiency, encourage your child to "help"you clean-up, if he or she seems willing (but make hand washing afterwords a required part of the process).
WHY ACCIDENTS HAPPEN
>STRESS. Separation anxiety, a new baby-sitter, a move, a new sibling, and family distress can all trigger accidents, even in children who have been clean and dry for awhile.
>FATIGUE. Tired children often have less control over all their skills, toileting included, and are also more likely to revert to "babyish" behavior.
>EXCITEMENT. Children often lose control of their bladder when they're can disrupt some of the concentration a child needs to remember to use the potty. They are more prone to accidents when they're engrossed in an activity.
>PARENTAL PRESSURE. A parent's preoccupation with toileting often turns off an independent-minded child.
>CONFLICTED FEELINGS. Some children wet themselves frequently because using the potty represents growing up and they don't feel quite ready to give up their status as the "baby" of the family. Others have "accidents" because they're reluctant to cede control to the older generation by doing what they know their what they know their parents want them to do most.
>POKINESS. Some toddlers have accidents or mini-accidents (they get slightly wet or soiled enroute to the potty) because they wait until the last minute and/or are slow in getting their pants down.
>URINARY TRACT INFECTION. Sometimes, a urinary tract infection can make bladder control tricky for a young child. An infection should always be considered in a child who's had no success "holding it in" (but seems eager to try) or has had success followed by sudden regression, particularly if other symptoms are present.
>A PHYSICAL PROBLEM. though such problems are very rare, it's wise to be on the lookout for signs that point to the possibility of one: The child who is always a little wet ( a sign that urine may be leaking), wets when laughing ( a sign of "giggle incontinence"), or has a weak urine steam, painful urination, or blood in the urine should be seen by the doctor.
Often, dealing with these causes of accidents (reassuring a stressed child, gently "reminding" a preoccupied one, seeing to it that a tired one gets more rest, treating an infection, and so) will put toilet learning back on the fast track.
WHEN AN OLDER CHILD RESISTS
When a toddler two and one half or older shows all the signs of readiness but after several months of parental effort, still refuses to cooperate in toileting, a parent may feel like it's time to get tough. But, actually, it's much better ---at least in the long run---to let up.
TURN IT OVER. Give your child full responsibility for toileting. Explain, "It's your BM and your urine, and you can make them on the potty when you want to. If there's anything I can do to help you, just ask me."
PRESENT CHOICES. Diapers or training pants, potty or big toilet, now or later. And keep your own opinions to yourself.
STOP REMINDING. As long as your toddler knows the routine, you needn't say a word about it. Anything you do say is bound to be held against you---and to delay potty learning even further.
DON'T TALK ABOUT IT. Make potty learning a non-issue after a while---don't discuss it with your child or in your child's presence.
SWEETEN THE "POT" Casually (as though it doesn't matter whether you toddler accepts the challenge or not) offer an incentive for success at the potty. If your child chosses stickers on a calendar, he or she can even chart the toileting "successes" of other family members so it seems like everyone's in this togeteher. Of course, if your child demands stickers or the present even when they haven't been earned, or gets extremely upset when a reward isn't forthcoming, you'll have to shelve this strategy.
ENLIST HELP. Often, a few words from a neutral authority figure, such as a nurse, doctor, or preschool teacher, are more effective than a thousand from a parent.
GIVE IT TIME. Eventually your child will decide it's time. Stop pushing for that time to come, and it will."