I used to sail at the train when I was learning and always just put my stuff in a bag and left on the sand, never once was it touched (that I know of

)
Now days I just put my car keys in my pocket, zip it up and go sailing. Its that easy, and before you say I can't put my fancy remote key in my pocket and sail, get a cheap stainless steel copy like I did, works fine & doesnt rust.

Although granted it doesnt stop someone watching when you get out on the water and then breaking into your car.