Here is a detailed answer about dogs. I wrote it on another thread for a person planning a transcon on a recumbent.
As for dogs on tour, I have had many experiences with them. Some cyclists might carry pepper spray, which I have done but never used. I saw another advise carrying a water pistol containing a mixture of water and ammonia; this I have never done. The fact is that dogs can be an occasional annoyance or hassle or whatever, but by and large they are not a real danger unless one comes charging at you from out of nowhere, startling you, and causing you to involuntarily swerve out into traffic. It happens.
There is something about the movement of cycling that sets dogs off into a headstrong frenzy of barking and chasing. I mean, you come along, and there is some dog in a yard. It has been lolloing around all day perhaps. It catches sight of you going by on your bike, and it immediately goes nuts. It starts barking, snarling, yelping, and growling, and chasing you at high speed and going for your heels with all its might. I have seen dogs go absolutely bananas at the sight of me cycling, even if I was two hundred feet away from them. I have seen them come charging out at me, stopped only by a fence around thge property. They would follow all along the fence line to the end, and then go ape trying to jump over the fence or tunnel under it. This kind of reaction comes from dogs of all sizes from the largest dogs to even those little Mexican Chihuahuas. That is no kidding. I was cycling through some town. Somebody was carrying one of those little Mexican dogs. It saw me. It went crazy trying to jump from its owners arms and chase along.
I have worked out a manner of dealing with dogs. In spite of all the noise and chases not one dog has ever actually bitten me. However, they do seem to be fond of going for the feet, and some have come close to biting. First, slow down a bit, look at the dog and yell out a loud, sharp report, and when I say loud and sharp that is what is meant; something like you might expect to hear from a marine corps drill sargent. You might have to yell a number of times. The yelling will bring some dogs to a halt. Some will stop temporarily and continue, and slow down or halt every time you yell. Just yell out hut or ha loud, sharp, and clear. If that does not dissuade the cur from pursuing his pleasure or whatever it is he gets out of the chase, come to a dead stop and give him the yell. He will stop. He may turn around and take off. He may tarry a while and snip and growl. He may come close, but my experience is the actual attack will not happen. I have cycled 37,000 miles through 19 countries, and six or more times across the USA, so I know of what I speak.
I have always ridden an upright touring bike, therefore, having a dog running along and chasing at my heels is a different matter from riding a recumbent with the animal more nearly at the vital parts such as torso, head, and throat. My general advice is this. If you are concerned, do what I have told you, and carry a water pistol with water and ammonia in it, if legal to do so, or a very good pepper spray, not one of those little key chain things, but a canister with a real fog or large volume spray that comes out, but do not use it as a first response. If you yell and stop and yell, the dog will stop his pursuit. In other words, do not run and it will not chase. Often, as you are stopped at the roadside waiting for the animal to lose interest, its owner will come out and call it back, and it trots on home. If you stop and it stops and loses interest, it might head back to its territory on its own, but if you take off it will turn around and continue chasing. Dogs, for the most part, are a temporary nuisance, but not a real serious danger. However, I am sure cyclists have been actually attacked, and perhaps even injured.
When stopped, the hound may come close, but will not actually sink its teeth into your hide. If it is particularly vicious or mean, give him a whif of the pepper spray or whatever, but I have never found that to be necessary. If you get off the bike and walk a ways, which you would not or might not be able to do, it could lose interest; get back on and cycle away, and it will pick up where it left off, or just go home.
Try not to let a dog catch you by surprise in close quarters. That happened to me once, and I tipped over injuring my ankle. It was at night on a quiet, placid road. A very large dog came charging aggressively from out of the bushes near the side of the road. All of a sudden I heard this very loud barking and snarling, and saw a blur out of the corner of my eye. In an attempt to stop, dismount immediately, and get the bike between myself and the attacking dog, I forgot my feet were strapped into the pedals, and tried to get off on the right of the bike, I fell over and twisted my ankle. Well, at least I fell over away from the dog and not toward it. After all that the dog just stood there looking at me, and turned around and left. It was one of the larger breeds of dog, and I am sure it would not have harmed me, but it caught me completely unexpectedly, and I reacted unthinking with a start. There was no time to think through what to do. The subconscious mind told me I was under attack and needed to respond, and I did.
You might have dog problems in some areas at times, and no dog problems whatsoever in other places. In 1984 in winter along highway 90 in Florida free ranging dogs were all over the place, and I might add, were often seen dead along the roadside after having been slammed by motor vehicles. In 2007 I cycled 90, and there was not the first problem with the first dog; very different from 1984. In countrified areas dog owners may be more disposed to letting their dogs roam free. Some may be fenced in, but have some little tunnel dug out under the fence in some bush-covered corner. They actually seem to be smart enough to try and cover or hide their tunnels. Anyway, that is about all I can tell you. If you go into Eastern Europe, you may find canines of a very different stripe; very different from the friendly domesticated kind we are used to in the USA. For some of those dogs I encountered in eastern Europe, nothing short of a 12 guage shotgun would save you.