I have watched on Youtube a video from a dog trainer who addressed this precise issue:how to deal with stray dogs when walking your dog. He advised any pet owner to have a pepper spray. It is for your dog's safety and your own as it is nearly impossible to break out a dog fight /attack once it is happening. 10 dogs versus 1 dog and its owner....not very good odds in case the pack goes crazy. Not even police trained dogs could fight a pack.
It is unfortunate to not be able to enjoy walks because other people abandoned their dogs or left them unleashed. I wish there would me more law and order when it comes to this, including in my own country
I consider getting a dog too later on and I have pondered the issue of stray dogs a lot. I will definetely go for pepper spray.