Hi
Carry a spray bottle owith cider vinegar in with you.
I have the same problem with off lead dogs,owners yell "hes alright" as it bounds over growling
I shout back "well mine isnt,hes had too many dogs off lead jump all over him so get your dog away"
I always walk with mine on-lead.They do have off-lead running but only down the stables,where i go every day,or places i know well and can see all around.
My dog will walk past other dogs,and will sit while i chat with other dog owners,but i always make sure i dont let other dogs jump on him.
His behaviour has got loads better and he even has his good citizen bronze award.He did it at a Champ show after his breed class,and was the only one, out of 9 all breeds,who passed
Have you tried clicker training?It may help with the distraction when you meet other dogs,but i would try to avoid the areas and the times, when you know there will be loose dogs.
I still walk the same areas but just do so early in the morning and later in the evening.
Good luck
Mel