Well I am at a lose as to what to do but really feel for you, terrible situation for sure.
I am guessing there is no leash law there so reporting that would not be a option but if there is one keep reporting and maybe the owners will get the message.
I like the camera idea though so you have proof as to what happens when it does.
My first thought was to just shoot the dogs but then realized that would just cause all kinda of other issues just like you have described
Could you carry a smaller caliber gun with rubber bullets so they may not kill the dog but scare the heck out of them? I dunno, no gun expert here.

I like the response to mace the owners, I had thought of that too. (I know it is isn't really an option but still)

What ever happens I sure hope it is good for you though. Not riding would not be an option to me so I hope it is not one for you.