I hate mean dogs that are not on a leash or behind a fence. I can say that because I've been chased plenty of times while out running. I was even bitten once, by a chihuahua - of all canines! It was a vicious little thing that nearly tripped me, but before I could step on him, he sank his fangs into my calf. Ouch! I was hobbling for weeks because the little thing pierced my skin and it must have bruised my muscle. I should have kicked it into the next yard, but I never expected it to bite.
Still, if there is anything dogs love to chase more than runners, it's cyclists. While out cycling, I have come across a few of these ferocious Fidos, but usually their name is something like 'Killer' or 'Diablo' and they are some pit bull mixed breed that can run really fast.
There are many reasons dogs chase or attack runners and cyclists. But some advice I was given by my veteran cyclist buddy, Roberto Lara, is if the animal gets close enough to you, squirt them in the face with your water bottle. He says that will send any dog yelping in the opposite direction. I haven't had to try this yet, but I'm sure I will.
I could carry a repellent spray or mace with me, but most of the time, I'd probably forget it at home. Or worse yet, by the time I actually needed to use it, the nozzle would be clogged up. Overall, I found Lara's advice worth trying in a desperate situation, so I thought I'd pass it along to you as well.
Of course, in Texas, some runners or cyclists might feel safest protecting themselves a-la-Governor-Rick-Perry's style and carry a "Coyote Special" to take out an attacking dog. Not sure if I'll fall into this category anytime soon, but it worked for him.
Happy running and riding!
