Siphon Gas?

I had a problem with gas being stolen out of my punt I always carry a spare 5 gal can with me .they would steel the gas and put the can back so I filled the can with gas and 2 quarts of corn surup a couple days later this young guys sea doo was broke down and his car was broke down on the side of the road . I drove by him laughing and waveing never lost anymore gas after that .