On my morning ride into the office, I was on a MUP along the Muddy River in Brookline/Boston. I wasn't going hard, but it was a good clip. I see two women with dogs up ahead. The women and one of the dogs is on the left, and the other dog is on the right. I don't think much of it until I see a VERY thin dog leash stretched across the path, about 2 feet in front of me. I immediately hit the brakes and come to a full stop. The woman holding the leash drops her end. The dog didn't move. The leash ended up between my fender and wheel, with some of it caught in the front brake. No tangles, and easily removed. Everyone is alright. I acknowledge that I should have seen the leash (though that leash was SO thin I'm not sure how). The woman acknowledges that she should be more careful with where she and the dog are on the path. No harm done.
The amazing thing is that I have clipless pedals, and have been using them for only about 4 weeks. I didn't have to think about pulling my foot out of the pedal. I just did it naturally. I guess I've gotten used to them.
Just keep an eye out for those leash hazards. It was a close call, but now I know to watch for such situations.