Here is an idea to make sure your magnet sticks around.
Get a list of local important numbers in the area.
Town numbers like the mayor, police, library, water and sewer dept. You can find most of these on your towns websites.
Then list other numbers like local pizzerias, sub shops, and others.
Maybe get a local electrician, plumber, carpenter, roofer etc. They could potentially help you buy some of these magnets and hand them out themselves as well, to help offset the costs.
Then have a section for lawn care and list only your phone number.
Stick these on doors in your area and be sure that your number will stick around for quite some time.
You could also have different discounts for services through out the year.
Join this discussion further at the Gopher Lawn Care Forum.