Living in a rural area, I've always carried pepper spray that I buy at a bike shop. For years, I was reluctant to use it, but two situations caused me to change my mind, and I now use it anytime I can on a chasing dog. Why the change of attitude?
Twice I have had a dog run out towards me, from the other side of the road, crossing the lane of traffic. One was a large dog, that was hit and killed by an oncoming vehicle. On another time, 3 smaller dogs ran towards me, and one was hit, but not killed (at least instantly). So I've made it my mission in life, to try and break dogs from chasing bicycles.