I'm not a doctor.  What follows should not be considered medical advice.  See you doctor first.  What I want is to save other runners some grief by reading my experience, and give them hope that it will get better.

Okay, ladies.  Let's talk.  Let's have a truthful and brutally honest chat about running, particularly what can happen as we get older.  If you've had babies, you already know what I mean.  If you haven't...you still might know what I mean, and if you're smart, you're already on top of it.  Yep.  We're talking Kegels, people.  I'm going to start by admitting that I never did them.  Never had any problems, ran for years quite happily, saying "feh" to rest stops.  I've had a couple babies.  I remember the nurse midwife mentioning something about Kegels to "strengthen the pelvic floor," but I didn't listen.  I was young.  I was going to bounce back.  Flash forward to about 7 years after my youngest was born.  One day I thought I was going for a training run...but wait...what the heck?  I'm not embarassed to admit it.  Its a common problem for women as we age.  I know other women who won't run at all for this reason.  I just didn't think it would ever be MY problem.  I pride myself on being a tough chick...but this is not a tough chick problem, right?  Wrong.  Long story short, I ended up at the PT.  Note here: see your doctor first, to rule out any major problems.  Chances are you just need some strengthening exercises.  But here's the kicker with Kegels...you have to do them properly!  You can Google "Kegels" and get some good information, but most of what you will hear just says to do Kegels like you are stopping the flow of urine.  Well, let me tell you, that little tiny muscular contraction is not a proper Kegel.  The pelvic floor is more than just one layer of muscle.  A proper Kegel consists of two motions.  Think of it squeezing together, and then pulling up and in.  And its not just a little contraction.  I'm going to be blunt here...its a more of a big movement where you are squeezing not just the "urine stoppage" part of the muscle, but all the "stoppage" parts of the muscle (aka your booty, too!).  When I first started doing these, I could barely feel anything.  Its important to sit or lay quietly and really concentrate.  It should feel hard.  You can't be lazy about it.  And here's another thing the good old internet won't tell you...if you want to help your symptoms, its not just Kegels.  There's a very important muscle called the transverse abdominus, or TA.  It lies deep in the abdomen, and wraps horizontally.  Its a low back stabilizer...like a  natural weight belt.  It "sucks you in" (forced expiration), and works with the diaphragm and pelvic floor region.   The TA is going to keep everything together, sucked in and tight.  Now, after babies the TA can get a little stretched out and it might not go back to the way it was.  You do crunches, ab exercises, etc., but most likely the TA isn't doing much.  Instead the big rectus abdominus muscle is taking over.  Rectus is a forward flexor, and boy does it look great on bodybuilders and anyone who is lean.  But rectus isn't going to help you.  In fact, when you are running, rectus can actually kick in, pushing down on the bladder.  And if TA isn't there to support it, and keep everything together, guess what?  Yep.  Add that to a weak pelvic floor and you're in deep with the stress incontinence.  Raise your hands if you know what I mean. 
So what can you do?  First, see your doc.  Again, its important to rule out anything major.  What I'm going to tell you as an avid runner is this old adage...an ounce of prevention is worth a pound of cure.  Do you Kegels NOW, before problems arise.  If you are one of the lucky ones, this might not ever be a problem.  Why chance it?  If you're just starting to have some issues, Kegel away ladies!  Remembering, focus on squeezing together and pulling up and in.  When you are first starting, its tricky and surprisingly difficult.  Stick with it.  Do 20 a day, and as you get stronger, up it to 30, then 40.  Do them sitting or laying down at first.  As you get stronger over the weeks, do them standing.  Another important note here:  keep your belly quiet when doing Kegels.  It should be a pelvic floor contraction only.  If belly kicks in, rectus is going to push on the bladder.  Not good.  Keep belly nice and quiet.  When you move to standing Kegels, this is especially important.  Take the time to concentrate and do them right.  You might even place a hand on your core to make sure its staying quiet.  Move on to graded contractions (squeeze part way, then all the way).  Eventually you can move to doing Kegels with one foot up on a short stool, standing on a couch cushion with the other leg.  You're not laying down when you're running, so its important to get the pelvic floor used to working in different positions. 
Next....work the TA.  Plank on your knees is a good place to start.  Go for 30 seconds, then work up to 2 minutes.  Eventually you will do full plank.  Remember, focus on the lower abs, keeping them tight.  Rectus might kick in a little, but think of your lower ab muscles working.  One note here about the TA:  it can be hard to find.  When you are first starting out, try standing next to a counter, feet hip width apart and knees slightly bent.  Place your fingers underneath, and pull up slightly.  You should feel TA working.  Try to make this brain-muscle connection.  Picture those muscle fibers sliding together.  Hold for a few seconds and let go, repeat.
Another muscle that is important, and underdeveloped especially in road runners is the gluteus medius.  Gluteus medius does abduction, assists in hip flexion, and also internally and externally rotates the hip.  What does that mean to you?  Its reponsible for side to side movement.  And as road runners, we don't do a lot of that.  Strengthening this muscle is going to help complete the picture.  One exercise to try:  lay on your side, knees bent.  Raise the knee toward the ceiling (think clamshell).  You should feel it in the back of your hip (the muscle attaches to the femur, or hip bone).  This is another surprisingly difficult move and you should start with 5-10 reps.
What is stated above is all from personal experience.  I'm not a doctor, or a physical therapist. If you are having problems, see a doctor first.  What I am is a runner who wants to run for a lifetime, with dry pants and a happy body.  This is information I think every female runner should know.  And I can tell you from personal experience, this works!  Like any training, it will take time and consistency, but in the end, hard work pays off.