Last year I was bitten twice by dogs during my hikes. The first time by a large dog that was on a leash but where the owner had insufficient control over the dog, probably because of its size and weight. The dog bit me severely in my left under arm. The wound was deep and wide so it needed to be stitched. Normally they prefer to leave a dog bite wound open because it infects easily but that was not an option in this case. 
The second time I was bitten in my calf by a dog that was not on a leash and where the owners were closeby. When I was past the dog it attacked me from behind. The wound was only skin-deep so not really a problem. 

Since then I have thougt a lot of means to defend myself against aggressive dogs. I changed my behaviour and I bought a dog deterrent via Amazon. I have two dogs myself so I know when a dog is aggressive or just wants to play. I am still not afraid of dogs but I became more careful when I encounter a dog.

A dog deterrent

There are several means to ward off dogs. Mace is an obvious choice but that is forbidden in Curaçao and is very aggressive against the dog and has a long-lasting effect on the dog. Another kind of caustic spray (eg based on vinigar or lemon) is also an option and can be self made. The problem with this is that the dog needs to be so close that you can effectively spray the substance in its eyes which is a bit too close for my comfort. Knifes, machetes are an option but they create a bloody mess and are generally not appreciated by the owners, so instead of an angry dog you have a confrontation with an angry owner. A stick is a good option if you like hiking with a stick. I tried hiking with a stick for that reason, but that is not a good option for me because I take a lot of pictures during the hike and I use my phone for guidance along the trail. So too many objects to keep in my hands. And I don't like hiking with a stick as long as I don't need a stick for stability. 
After searching the Internet I came up with loud noises as a deterrent. There are two options: a noise that is only loud for the dog and a noise that is loud for dogs and people. The latter has the advantage that it is clear when it is used, the first one you have to trust because you hear nothing yourself. I have ordered both from Amazon. Up till now I trust the ultrasound version but I have the horn as a backup.

An ultrasound deterrent

Dazer II Ultrasonic Dog Deterrent device web

The explanation on the back of the package is as follows:
The Dazer II hand held ultrasonic dog deterrent is useful for anyone wanting to avoid contact with dogs. The Dazer II is a humane alternative to chemical sprays, physical force and other deterrent methods. Using the latest ultrasonic technology, the Dazer II creates  an uncomfortable but not harmful, high powered sound audible to dogs, but not to humans. A simple 1 to 2 second activation startles the dog, instinctively deterring its approach from as far as 20 feet. 

The device has a visible diagnostic indication so that you know that it is working. This indicator also acts as a low power warning. The device is powered by a 9V alkaline battery that should be sufficient for 1000 one second activations. 

My experience with this device is that it works. It will not stop a dog at the promised 20 feet (6 meters) but it will stop the dog. My most recent experience was with three aggressive dogs together that attacked me. Finally it stopped the dogs at about 5 feet. The fact that this was a group of dogs certainly played a role. If the group would have been greater I suspect that the device would be even less effective in halting the attack. Luckely you normally encounter only one dog.
The owners are not pleased when they see you using the device and seeing the effect on their dog but I consider that not a real problem. They should have had their dog on a leash to begin with.
The device has a clip so that you can easily attach it to your belt or pants.

If you encounter an old dog it could be that the device is less or not effective because the hearing of the old dog could be impaired.

This device is available via Amazon; unfortunately Amazon does not deliver this item to Curaçao so you will need a forwarder in the US to get it to Curaçao. 
The link to the device on Amazon: Dazer II dog deterrent. The price is $30.95. 

A loud horn, Doghorn XL

Dog Horn X webL

The XL stands not for a big size but for an extra loud horn. For the size I have put a small matchbox next to the package.

According to the text on the package this device will stop most dogs in their attacks. It also repels most wild animals and birds, so it is great for campers, hikers and for any outdoor activity. To use it you have to point the device towards the animal and activate a blast while backing away slowly. Repeat if necessary. The sound alerts also for help.

I haven't used this device yet so I have no experience with it. The only experience is when I activated it for a test and I was surprised by the loudness of the horn. It is really really loud! According to the specs it would be 110db. So I guess a dog will be startled and stop its attack. 

According to one of the answers on Amazon the canister would suffice for more than 140 short blasts. 
This device has a clip so you can easily attach it to your belt.

This device is available from Amazon; you will need a forwarder to get it to Curaçao because Amazon has no delivery option directly to Curaçao for this device. Refills are also available from Amazon.

The link to the device on Amazon: Doghorn XL. The price is $12.59.

Changes in my own behaviour

Because I was bitten the first time by a dog on a leash I try to stay farther away from dogs. Just as people also a dog has a comfort zone. As soon as someone enters its comfort zone it will defend itself if it feels threatened. That is wat probably happened the first time. I had to pass the dog and owner and apparently came to close according to the dog. Of course the dog should have been trained not to attack people and the owner should have kept the dog on a very short leash. But I have learned from this experience. I am more careful when I encounter dogs.

  • Try not to look directly at the dog; it could feel threatened by your stare
  • Try to determine if the dog is playful or aggressive; lots of dogs will come towards you just because they are curious, not because they want to attack you. Most probably you will be able to see the difference in its behaviour but always be on guard
  • When I see a dog (with or without owner, on a leash or not) coming in my direction I will stop and step aside of the path if possible. But at least I stop. Most of the time the dog will pass without a problem but I am watchful without looking directly at the dog. 
  • When I see a dog before me walking in the same direction I slow down and don't pass the dog / owner
  • When I have to pass a dog because it is walking too slowly I try to keep it in my view without directly looking at the dog. Some dogs feel free to attack from behind especially dogs without an owner but my second bite was from behind by a dog while the owner was watching.
  • When I don't trust the situation I have the dog deterrent visibly in my hand and ready to use