How to lock kayaks to roof rack

Double Kayak Roof Rack Holds 2 Kayaks - StoreYourBoard.com
Double Kayak Roof Rack Holds 2 Kayaks - StoreYourBoard.com
ECS News - B6/B7 Audi Sedan Roof Rack Base Bars
Kayak Roof Rack with Load Assist Malone SeaWing Stinger ...