Dogs wearing armor has a long history. In fact some still wear it today:I remember when I worked in the pet industry hearing that adult, active dogs can carry no more than 25% of their weight without risking injury. In my mind, it's pushing things to even consider having a fully armored Halfling on a dog for any period of time, and then to add plate armor as well? That seems... unlikely.
But hey, I'm no expert and more importantly, it's a fantasy game, have fun!![]()
Riding a dog is a different story, their spines aren't made for it. Then again we're talking halflings and gnomes so maybe?