Do you offer a discount for frequent clients?

I have some clients whose dogs I walk every workday, in one case multiple times a day (small dogs with small bladders). My loose practice has been to offer a 15% discount off my posted rate to regular clients who are booking three or more services a week. It's more efficient and easier to schedule for me to get weekly bookings from old clients instead of playing email tag and going on meet-and-greets that might or might not work out. From the client's point of view, it's a real financial burden to pay for pet care every day in order to go to work, rather than as a rare expense associated with optional activities like going on vacation or doing something in the evening.

I was wondering if other sitters do anything similar.