Been a dog owner/lover i would recommend taking maybe a cheap pack of dog treats along walks with you you can buy them for 50p.And throwing treats on the ground to a dog,also a spare slip lead and if possible catching any stray/aggserrive dog with the treats and lead then calling the local dog warden.As any owner who allows there dog to be unattended and esp an aggresssive one shudnt be allowed a dog.Just kicking or chasing the dog away couls result in it scapering off elsewhere,been shot by farmers,run over or biting some kid ect...and all because none of it is the dogs fault.
It simply shudnt be out alone.