Being a boater I always seem to use a 1" cam buckle strap for all my strapping needs. The cam buckle is pretty stout and secure. I used a 1" cam buckle strap and a bicycle combination lock to secure my water cans to the top of my fuel can rack. Here are a couple of photos to show you what I'm talking about.
Right side showing the 1" cam buckle strap and the bicycle cable lock
Left side showing how the strap loops around the rack and heads back to the buckle.