I've been advertising through vets, pet stores, and online since I started this two years ago but now I think it's really important that I hand out my cards in person, as to make more of a positive impression.
*Edit: I DO offer dog walking services for regular clients. In fact, ideally I'd love to get some regular dog walk clients going for the summer since two of mine have decided to cancel services to save money. Also, if of you DPer's are interested in services, here ya go:
Right At Home Pets
(I'd be open to offering a DP discount too!)