So, my dad has been a serious cyclist for 10+ years now. Riding in rural areas is both the best and worst thing for a cyclist, and I'm assuming runners as well. It's so bad because there are so many dogs that are considered "farm dogs," who aren't really trained as family pets, and obviously aren't leashed/tethered, and they obsessively passes their properties. I live in a big midwestern city that has farmland in every direction 40 miles out. When you go on 100+ mile rides...you go pretty far out into the country.

Basically, my dad was almost knocked off his bike by a pack of dogs once, and he started carrying a heavy stick to basically fend dogs off with. He was mostly okay with squirting them with his water bottle to startle them enough so he could get away, but he was always scared he'd be mauled on a back country road.

If it's a popular road for cyclists/runners, I can guarantee you you're not the first person he's come after. I would highly advise you to at the very least carry a waterbottle you can squirt him with or whack him with if you absolutely need to. If you'd feel safer carrying some kind of mace (I know they sell dog repellant spray on amazon specifically for this), I think you should do that.

I'm not sure calling the police would do anything, in rural areas things tend to work a bit differently in regards to dogs and cats. I'm not sure how it is where you are, but if you called the cops on someone's dog being off-leash in a rural area after-the-fact, you'd get laughed off the phone. If you know the neighbor, I'd go over and talk with them, just mention how it scared you to have their dog chase after you, and ask if they'd be willing to leash him or keep him within a fence from now on.