Citronella won't work on on aggressive dog bent on attack. Trying to beat it with a stick may get you injured, too. Remember, all it takes is one shake by a predatory dog to break their neck. You won't have that much time if you are attacked.
I have carried Mace's Muzzle ever since a loose dog snuck up behind Lady and I. I fell on the frozen ground and broke my pelvis trying to save her. Thankfully the dog's owner was right there (a child had let him out).
I have never had to use it and hope I never do. I worry about it getting in Lady's eyes, too, if I ever needed to, but if it saved her life it would be okay. It just stings, but doesn't do any permanent damage.
Amazon.com: Mace Brand Muzzle Dog Repellent...