That's a great question, and a common headache for anyone dealing with curious animals or windy days! The "most secure" lock often depends on your specific problem, but a few types stand out.
For ultimate security against determined animals like raccoons or bears, a heavy-duty shackleless padlock or a heavy-duty combination lock is top-tier. These locks have a thick, hardened steel body that fits through the bin's latch, leaving no exposed shackle for animals to pry or bite. They are incredibly tough to defeat without tools.
If convenience is key, a built-in combination lock bin is a fantastic choice. These specialty cans have a dial integrated into the lid. They're weatherproof, easy to use in the dark, and eliminate the worry of losing a key.
For general wind protection and discouraging casual pests, a simple bungee cord with a lockable hook or a weatherproof keyed padlock works well. The critical factor here is ensuring the lock is weather-resistant (stainless steel or coated) to prevent rusting shut.
My personal recommendation? For most suburban areas, a sturdy combination padlock offers the best balance of security, convenience, and durability. It deters animals, survives the elements, and you never need to hunt for a key when taking out the trash.