One common problem is typically a pedestrian does not know a cyclist is passing from behind. No mater what you do some peds are startled when you announce yourself, or when you pass. Nothing works every time. Some things work part of the time. I don't want to start another thread about what works, there are too many of those already. I just have an idea that I have not heard about before.
Another problem is dog walkers on bike paths, MUPs, and other places when bikes are allowed too. Including dog walkers near the road. Even with a short leash (the short leashes I have seen were 5 feet long, add a surprise pull to extend the owners arm and you have another two feet or more), if a dog sprints after another animal at 90 degrees to the walker, the leash can go right in front of a cyclist. Some of the self coiling leashes are 21 feet long (plus arm length) and the path and the grass on both sides can be blocked in an instant, if the dog owner is not paying attention 100% of the time. A dog on a sidewalk can sometimes make it into the road.
When I ride I always wear my "Take-A-Look" mirror. I always know what's going on behind me, I scan 360 degrees almost all the time. With my mirror I can actually look forward and backwards at the same time.
When walking along the grass next to the bike path the other day I realized that if I was wearing my mirror I would not have to turn around often to see what's coming if I am to move over. With the dog it's even more important to know what's coming from behind. My mirror fits on my glasses temple and that's where I wear it.
1) Pedestrians, especially dog walkers on bike paths should wear rear view mirrors and practice until they are proficient. I will be doing this.
2) All dog leashes should be a high visibilty color like international orange. They should also have reflective material in them (some do). Black leashes should be illegal !