Don't believe the urban legend of spraying Pam underneath the deck!!! I even tried a teflon-based dry spray lubricant called Zeplon on a brand new lawn tractor deck.....no joy. I've heard that painting the deck belly with Emron paint(used for painting airplanes) works but it's a hazmat and not a DIY project. Raising the deck, using a putty knife and then spraying with a garden hose after each mowing like you stated is the best method. Once a season, before storing, jack it up and power wash it. Also, after each mowing...be sure to let it cool down before spraying that cold water on the deck spindles. For the rest of the machine don't spray often with water...just use a power blower. Again...a nice wash & wax once a year before storing for the winter won't hurt.
P.S.
If a manufacturer decides to build and sell a mower with a "teflon coated" deck belly they would break all sales records and all others would scramble to follow suit. Of course tire manufacturers have the ability to produce a tire that would yield > 100,000 miles but sales would go way down....right? Same goes for "lifetime" build-up free decks on ZTR's:0)