Nature's call on the training trail
Have you ever had burrs on your butt? Once, several years ago, while making a dash into the bushes on a training walk, I failed to notice that those bushes had burrs. There comes a moment of desperation when you don't care so much about the details of bushes, you just need some cover to answer nature's call. In truth, bushes are a much happier place than many port-a-potties i have visited. It certainly smells better in the bushes.
Still, burrs can be problematic, especially when you discover hundreds of these sticky free-loaders have found a home on the inside of your training pants. They don't improve the comfort level of the rest of the walk and they are a nightmare in the laundry.
So, my best advice is to plan the training walk within the parameters of clean, public toilet locations. Gas stations are a popular stop but they aren't reliably clean and there is always the possibility that the dreaded "Occupied" sign is on the door as you arrive in a desperate state (they usually don't offer multi-stall bathrooms). Tim Horton's and MacDonald's are probably your best bet - they're clean and there are usually multiple stalls. Hotels can be tricky. We look suspiciously unlike hotel guests when we enter covered in 10 winter layers, including a balaclava and Yaktrax. But, oh, if you can get away with it, there are some pretty sweet opportunities for a a moment of luxury - the privacy of floor to ceiling walls, cloth hand towels, possibly hand cream.
As a final word of caution, avoid hiding in any bushes surrounding large public buildings that may be video taping your activity.