I always took it as being a way to cover his own tracks (if an animal did it, he wouldn't be a suspect by default). Holmes himself points out that without tying him to the hound (which he had hidden really well and could theoretically put down and hide in the swamp if need be), there's no case against him beyond the flimsy circumstantial evidence.

While convoluted, the plan was more or less effective. The slip-ups that led Holmes to the truth were plausible ones that could be worked around (and the only one that really was his carelessness was telling Watson that he had been a teacher, since Holmes was able to use that background check him and figure out who he really was).