I just purchased this and love it: INNO INA446 Surf-Wind-Long Board Locking Roof Carrier w/Board Pads - Holds (1) Kayak or (1) Canoe or (2) SUP/Wind/Surf-Boards https://www.amazon.com/dp/B005W1BP4M/ it's super easy to install and then use when tying down your board. It takes me less than a minute.

I previously had the Thule SupTaxi which sucks -- the strap does not properly feed through the locking mechanism (don't get the SupTaxi)