As long as the owner keeps trying to get their dog under control I don't have issues. But if I'm being polite trying to keep my dog and horse out of their way - I do expect them to be intellligent and do their utmost to get their dog under close control, not call it once continue with their jog and ignore the subsequent barking when their disobedient dog comes down a side track to investigate my dog who is standing in close position next to his mum and pony. My dog was badly bitten by another 18 months ago and avoids other dogs if possible rather than get in a shouting match, consequently I try not to come into close contact with other dogs if avoidable. We also got chased by a young boxer who just thought it was fun. 'Dad' was left calling and puffing far behind. I took the risk of stopping and the dog then heard her call and returned, but a bit of forethought by the owner seeing a galloping horse on a different track and the dogs ears going up, might have avoided the situation.
I am well aware how much effort it takes to train a dog properly, teaching mine to follow at hock involved many hours of intensive work on foot using a long rein tied around my waist so that he was pulled up short if he went after stock. I spent a lot of time on my arse, but he understands LEAVE, NO, and PONY extremely well.
So yes, other peoples lack of control of their dogs does spoil my riding but many owners are brilliant and friendly, others try which is fine its just the ones that don't bother really get up my nose.