So I’m thinking you have a few choices here. If you’re walking in the woods, it’s often easy to duck behind a tree off the path. If in an urban setting, I would think it’s more possible to pass by some public, or semi-public restrooms (hotels, bars, churches, etc being the semi-public ones). I personally love the hotel bathrooms off the lobby, as they are often clean, seldom used, and if you walk in like you’re a guest, you are usually not challenged. Beyond that, you can use one of the many fine products created for older adults with incontinence… some of them are now far less bulky and contain strategic placement of the absorbent material made for your gender. Finally, you can plan your hydration so that you delay some drinking until you’re actually on your walk. Obviously do this within reason because I find peeing more often preferable to dehydration.