Have the same problem on a short stretch of my commute to work, some woman who thinks she is in the film "Born Free" naming her 2 Alsations Elsa and whatever the other one was called – you know the type jogpurs, wellingtons, barbour jacket and dog whistle to boot. After being chased numerous times by her huge dogs I confronted her to voice my concerns that if she was goingb to let such big dogs run free off leash then they should at least be muzzled. This didn't help as she know automatically sends them after me as soon as she see's me riding past, have thought of buying anti dog spray from Germany which is apparently used by there postie's, though I think it's just pepper spray, not sure on the legality? Though a friend of my mine who's a bit 'Johnny English' said they use a mix of 20% water and 80% ammonia which used in a water spray bottle makes any dog think your the King Kong of the dog world and will s*@#t itself.