Chows can be dangerous...but any dog needs training.
My nephiew has raised several dogs over the years for coon and hog hunting. One of the most memorable was a mountain cur named Gus. Gus was very aggressive around other dogs, terribly devoted to my nephiew, and totally harmless around people.
One day a neighbor's chow wandered into his yard and began barking, growling, and making dashes at my nephiew. He ran the chow off with a large stick, and returned to working on his truck.
The chow returned, even more aggressive than before. During the entire episode Gus, who was chained up, was apoplectic with fury. Finally, as the threat grew, Gus hit the end of the chain and broke it. The ensuing fight was epic...and ended with Gus killing the other dog.
My nephiew quietly disposed of the body and never told his neighbor what had happened...because the neighbor had been warned on several occasions that his chow had been threatening his neighbors.