>>60799592 (OP)
Honestly, the best part of being a dog-walker is finding huge intact large-breed enormously hung dogs to take home for an hour or two of intense "exercise". Then you bring the dog back and the owner is so appreciative that you gave their dog a long fun "walk".
You can build this up to maybe four or five dogs, gotta pick them up separately though, so you won't get rich off this, but you'll be thoroughly satiated. The dogs will never tell on you.