The first seconds set the tone
When a loose dog comes at you fast and its owner is absent or shouting without effect, your instincts will say run or haul your dog away. Both make it worse: running triggers pursuit, and a suddenly tight lead tells your dog the situation is dangerous and he should react. Stop moving, turn side-on so you present a narrow, unthreatening profile, and keep your own dog beside or slightly behind you with a loose lead. Speak in a low, boring voice. Many charging dogs are bluffing or over-aroused rather than committed, and a pair that stops and turns away stops being interesting.
Put the world between the dogs
Look immediately for a barrier you can step behind or put between you: a gate, a fence line, a parked car, a bin, even a hedge you can back against so the other dog can only approach from the front. Swinging a bag or coat in the gap can slow an approach without striking the dog. A handful of treats thrown hard at the ground near the charging dog's feet often halts it for crucial seconds while it sniffs and scatters its focus, giving you time to walk calmly out of its territory. Umbrellas opened toward an approaching dog work the same way, as a sudden visual wall.
If the dogs meet anyway
Avoid the most common injury in these encounters: hands grabbed into collars between snapping dogs. Do not reach for either dog's neck or face. Loud sudden noise, water thrown over the dogs, or a coat dropped over the loose dog's head can interrupt some scuffles; wheelbarrowing hind legs is a last-resort method for a dog locked on, and only if you judge you can do it without being bitten. Once separated, create distance immediately, because dogs re-engage quickly while adrenaline is high. Check your dog slowly once you are somewhere safe, parting the coat to look for punctures hidden in thick fur.
Afterwards: bodies, reports and shaken nerves
Puncture wounds can look tiny and still be deep, so any bite that broke skin, any limp, swelling or unusual quietness afterwards earns a call to your vet the same day. Note where it happened, a description of the loose dog and any owner details, and report the incident to the local dog warden or authority, especially if the same dog is regularly loose there. Your own dog may be jumpy on that route for a while; walk it at quiet times, reward calm behaviour and do not force close encounters to test him.
Prevention on your regular routes
You cannot control loose dogs, but you can load the odds: keep high-value treats in your pocket on every walk, practise an emergency U-turn and a solid stand so your dog has rehearsed calm responses, and cross or turn early when you see an off-lead dog approaching with no owner in sight. Keep your dog's lead and collar secure enough that a sudden lunge or a scuffle cannot slip him free. If he does tear loose and run during an attack, KinsLe's Lost Pet Alert System can alert nearby members fast while you track his direction from a safe position.