kanulock
Surfboards or Paddleboards which are secured with KanuLock straps can not be slid out as the straps are reinforced with stainless steel. This also means they can't easily be cut with a knife, they make less wind noise and are very easy to use. Easily lock any board to any roof-rack.
Don't risk using regular tie-downs to secure your valuable equipment; anyone can walk up to your car and take your board within 10 seconds, without any tools and without attracting any attention.