Pup wont pee or poop on a walk

Question
Hi, I have a 5 month old, 40 lb shep/lab/chow mix, whom I have had since she was 11 weeks old.  She is housebroken and completely healthy and lovable in every way.  Her doggy run is part Astro turf where she can play and relax, and the other part is small pebbles and this is where we have trained her to eliminate.  We walk her several times a day, take her to play areas, hike, etc.  Although she has peed "in the wild", as we call it, a few times here and there, it is not a regular occurrence, nor can I count on it. She has NEVER pooped anywhere other than her run!  On the one hand, it saves on poopy bags and I am not picking up poo on other people's lawns, but on the other hand, how will this work if we want to take her on a weekend trip or a really looong hikes for hours?  Why does she not eliminate on her walks?  Will this change as she gets older?  I would love to hear from anyone else who has experienced this as I find it very unusual!  Thanks!

Answer
You have inadvertently trained your dog to potty only in one spot and you need to retrain her to potty elsewhere while on leash. No, this will not improve on its own, with age or otherwise. She will have a difficult time if you take her on a trip with you, and will hold it as long as she can.

Keep a journal so that you have a pretty good idea of when she usually eliminates, and start taking her for walks around that time. You might also try using a suppository on her just before you start your walk to encourage her to eliminate. If she does eliminate, praise the heck out of her.