My buddy opened up a kennel. He said during a good month, he makes 2K. Not worth the hassle and constant effort it takes to pick up steaming pile after pile IMO.
Here in the DC area those guys make very good money. Most charge upwards of $18-25/day.
I have a friend who pays $18/day for her dog...but they guy picks up her dog and several others (usually around 6-10 at a time) and takes them to a park and lets them run free for at least an hour. Then he drops them all off. He also will board/kennel the dogs for $45/night. Usually just dogs that are among his regular customers.
I'm not sure what you could get in Vegas area, but it wouldn't be a bad job. If you had just 6 dogs/day at $15 = $90/day...and if you board an average of 5 nights/month at $30/night = $150/month...you'd make around $2K/month. And that's minimal for basically a part-time job. Also, most of this could be done tax free (if the customers paid in cash). Liability insurance would be minimal and you could write off ALL miles and gas on your vehicle (the tax man doesn't need to know about the non-work related miles).
If you built the business you could hire a Mexican or some young kid to walk the dogs and keep half the money. You could have several dog walkers in fact.
You could offer additional services like dog washes, take the dog to the vet, buy dog food supplies for the customer, etc. And you could possibly get a blow job or two from some of the dog owners!
I imagine you'd get a Holiday/Christmas bonus from most of them as well which could be another $1000-2000/year.
If you really built the business you could get a car like they had on Dumb & Dumber!!