As we get ready for our cross country tour I have been doing a few check lists and one item is the above subject.
In our normal riding around NE Ohio we have been chased by dogs and we find it quite unnerving. I noticed at the LBS the product Halt.And have seen some people have it on their bikes.As a woodworker I was wondering about using my lathe and turning a slender baton that would be able to be accessed easily to ward off an aggressive canine.
Your thoughts and ideas are welcome!

Ak47

Throw cats.

If you want a lightweight, pain-inducing, striking weapon, an old car antenna works wonders.

I've seen people get more of those mace type sprays on themselves than on the dog. I've always been successful waiting to the last minute and giving the dog a good spray from my water bottle, normally scares the **** out of the biggest and toughest dogs.

Yelling a loud "NO!" works to at least make most dogs hesitate, so you can make your escape.

A guy I rode with last year told me that sternly telling the dog, "Get off the couch!" has great success.

Here are 4 links to information about dealing with dogs while bike touring.

One deals with rabies shots in India.

My personal approach is the same as BigAura's, yelling "NO!", "Bad Dog!", and "Go Home!" often works. Dealing with the dog owners is an entirely separate problem!

I've tried or seen most of these. None of them work every time.

Stop riding and get off the bike. The dog can't run in front of your wheel and crash you! The dogs usually just run up and bark. But if there's two or more dogs, they tend to circle around.
This is my usual response. But the only time I've been bitten was when the dogs just charged right in and nipped me on both legs at the same time. Then they backed off. It can take a while before the dog lets you walk out of it's territory. Yelling and squirting water can help.

A loud whistle. I've seen this work. The dog just stops in his tracks. Those "rescue" whistles are really loud! But I still don't carry one.

Yelling or roaring or command voice. Often works.

Water bottle squirt. This usually backs off dogs. It's good to keep barking dogs away, so they don't run in front of my wheel. My camelbak bottles are good for this, since the valve stays shut until I squeeze, so I can aim first.

Changing course and aiming right at a dog up ahead, while yelling. Sometimes this gets the dog well away from the road.

Pepper spray. I've never seen it used. Some of the group riders carry. I would bring it on a tour, and stop the bike, then spray if necessary.

Frame pump / stick / etc, a whack on the dog's nose. Never seen it used. It's been recommended on these threads.

Outrunning the dog. I'll only do this if the dog is way back in the yard and starting to charge out. I need a big head start before this is even practical.

Did some searching and came up with this Mace Pepper Gun Buy Pepper Spray

I have had some success with one of those air sirens like to ones they use at lacrosse games. The sound scare the crap out of the dog.

Just finished reading Every Inch of the Way, by Ton Bruce, last night. He used a Dog Dazer (below) with good effect when he first started out on his trek around the world. However, he makes no mention of it for the last 3/4 of the book though he does mention getting chased. Has anyone here given it a try?

Amazon.com: Dog Dazer II Ultrasonic Dog Deterrent: Pet Supplies

Off topic: those of you that are stealth or low budget campers might want to read this. The ebook has loads of pictures too.

An enthusiastic,"Time for a bath!" seems to send my dog running the other way.

something that can fit in a top tube bag, maybe a 9MM would be better?

Probably the best way to deal with dogs. I'd also add that you don't give them anything to chase. When a dog charges out toward you, yell "No!", "GET!" or any other phrase you like in as loud and deep a voice as you can. Then slow down or stop. While you are slowing or stopping, keep up the commanding voice and look them right in the eyes. Stopping short circuits the chase response. Dogs are cowards and aren't going to waste time on something that isn't worth chasing or is acting like it might fight back or acts like it's the leader of their pack.

Boker Wilson Tactical Para Cord Monkey Fist, Olive, Glow in the Dark (09WT103) - KnifeCenter

You might try the "monkey fist". It is a steel ball bearing wrapped in parachute chord.

It will knock the teeth out of a dog, put a dent in the hood of a car and repel "urban youth" that harras you as you ride by a city bus stop.

if you buy one of Bruce Gordon's hand made titanium frame fit pumps with the old Campagnolo steel P/V pump heads
there are 2 prongs to hold the pump head solidly over the BB shell ..
when it meets the canine cranium with adequate force it will make an impression..

and being Titanium rather than the plastic of the Silca Impero of the pumps it was patterned after
its rugged enough to still pump up your tires when the attack has become a rout and whining retreat .

sounds crazy but a childs water pistol works everytime,as well as an ak47

In my experience pepper spray has stopped some vicious dogs dead in their tracks. It's 100% satisfying to score a direct hit. I look forward to the moment a dog decides to chase me! when they are standing at the end of a drive way barking I yell, "BRING IT ON YOU COWARD!". Plus in the long run the dog learns to leave cyclists alone.

Well, probably not overly PC to carry a firearm - some areas that might be a legal concern
the various mace or pepper sprays, in some areas are also a legal issue.
What works best for me is about an 18" length of 1/2" rope with a golf ball or slightly
larger knot tied on the end. After a little practice, a tap on the dog's nose is pretty effective
discouragement.

Three years ago I did a solo bicycle tour in Romania and I had this same problem with a more sinister twist, that part of Europe has a very high incidence of rabies! It was suggested that I keep stones in my pocket and a long thin bamboo cane kept on easy reach. If the dog gets too close try to hit it in the face. It is possible to get rabies even from a dog scratch! As it turned out I never needed to use it, but I did feel better having it on hand.

add 10% ammonia for effect.

Dogs are usually not an issue. Based on the recommendation of our mailman, I've carried Halt II on several long trips. I've never had to use it on dogs, but it works well on thieving raccoons!

Ammonia is a winner but a steel lock cable works great and you can use it to lock your bike as well.