I had an amazing guy make one of me and my dogs fighting off monsters in a post apocalyptic city. https://imgur.com/01ZgAe5 You can also craft your dog armor for fairly cheap if you are willing to do the chainmail yourself.

Historically, they were most effective as a psychological weapon against unarmored people in skirmishes or raids. The Spanish conquistadors considered their dogs to be vital assets during the colonization of the Americas and utilized them in brutal fashion. Edit: Another thought.

Recently, I started to read book about using animals in ancient warfare, in chapter about dogs there was mention that in medieval war dogs were used against horses, but because this book in not about medieval there were no examples of sources.

The people of medieval Europe were devoted to their dogs; one great French dog-lover declared that the greatest defect of the species was that they ‘lived not long enough’.

The use of medieval dog armors wasn’t confined to Charles V’s court – they were crafted throughout Europe between the 14th and 16th centuries. Fashioned from leather, steel, or even boiled wood, these canine suits of mail served practical purposes.