I am not sure how old the 2 girls are,but a can of mace or a stun gun [if legal] are 2 decent choices for self defense against bad dogs and bad people.
however the safest way is to keep the dogs at a distance IMHO.
too bad you couldn't get together with the dogs owner and request to ''meet the dog''.
who knows maybe that way the area could retain a peaceful vibe instead of a dangerous vibe.
best of luck for a peaceful summer!!!
Teana- black & red GSD (rescue)July 10, 2013
CHANNING American white shepherd
-Min-Pin 1-10-01 until 2-12-14