Peper spray might work good, its got some range too.

for big dogs that are strong and aggresive It hink they might just ignore it... for that I recomend a very strong tazer. Instead of a gun as we talked about on some other threads, I think I will have one of these since I can use it if needed and not have to kill who/what ever is after me... that just looks bad on your paper work and I would hate to deal with the cops.