Despite having a strict leash law, I am constantly amazed at the number of dogs I encounter on our mountain trails. I ride daily and put in 100K a week or more on our 2 horses who are being riden distance/endurance. It's unsettling to be in a long trot or hand gallop and any kind of animal pops out onto the trail.
I honestly don't mind the owners who are aware of their dogs whereabouts and quickly call them to leash, however, I have very little tolerance for those that think it is interesting to see how their dog reacts to a horse on the trail whether it be barking, approaching or even chasing. Luckily my horses are very dog proof (we have 3 of our own) but I have had to turn-to-face several times and once had to advance with my dressage whip in-hand when I had an aggressive dog approach us. I invited the owner to my farm to introduce his dog to horses but he didn't appreciate the fact that my horse was going to strike his doggie and I was willing to lay a whip on his beloved Rottie mix. I have taken a few license plate numbers of rude offenders at the trail heads over the years but most of my "regular encounters" are always worth of a little break to say Hi along the way.
Ten years ago I quit taking my border collie along when I was cited by the Forest Police for not having her on leash. He explained top me that the dogs roaming free encroach on and scent in the deer habitat and that the cows will not feed on the pasture grass where a dog has done it's toilet. I had to pay a big fine of 200$.
I do take them up for a bit of exercise but I walk or they run next to the Quad. We do stick to the trail on leash. On the farm they are free to run around all they want.