These dog threads are pure poison.
Unfortunately, the economic situation has caused a lot of folks to lose their homes. They can't take their animals with them when they go into rented property like apartments. In many places, they charge for placing animals in the pound. As a result, the poor animals are abandoned and hungry.
They soon form packs and become dangerous. Just last year, a pack of feral dogs attacked and ate a groundskeeper at a local park. And I just read last week that a lady in New Mexico was killed and eaten by loose dogs.
Calling animal control is absolutely pointless. They won't do anything unless the animals get on to the freeway or attack someone important.
Firing warning shots at a dog is pointless also. Dogs do not understand firearms. It is just another noise to them if you do not hit them.
The answer is good fences and vigilance. Keep a close eye out for them. Then if they make it through your fences, shoot them.
Good luck,
Rufus