Most of us love a good parade, so give dog owners the chance to show off their pride and joy.
Get some sponsors for your event who are happy to donate for dogs who complete the route (or for every mile walked). A scenic park or downtown area will work equally well for the parade (though you might want to see if you can close a local street or two to minimize disruption. If you want to go all out, parade down Main Street having closed it to traffic with all the dogs wearing their own tailor-made costumes.
If you have puppies and smaller dogs involved they can be pulled along in decorated wagon floats. You're going to need pooper scoopers and trash bags on hand as well for the people on poop patrol.
Refreshment stations along the route with water bowls and treats are a good idea and you can make the same provisions for the human companions at the same time.
You might want to set up a side fundraiser such as a dog bakery offering homemade treats for sale. A dog washing and nail trimming service is another good idea you could incorporate if you can find local groomers willing to donate their services. You can then ask for donations of $5-20 for people wanting to give their dogs a makeover.
I love all these funraisers they gave my some good ideas and some bad it was so much fun to do a funraisers