That's a great question, and a common challenge for homeowners and businesses alike. The "most secure" system really depends on what you're trying to keep out—whether it's curious animals like raccoons and bears, or unauthorized people. For the highest level of security, a multi-layered approach is often best.
For deterring intelligent animals like raccoons, specialized locking lids or latches are key. Look for bins with integrated, hands-free locking bars or clips that automatically engage when the lid is closed. These are often more effective than add-on solutions because they're built specifically to resist clever paws. For larger animals like bears, you may need a certified bear-proof container, which typically uses a complex latching mechanism requiring dexterity to open.
When human access is the primary concern, a heavy-duty padlock and hasp system is the classic, most reliable choice. Use a weather-resistant, shrouded padlock (like a disc or shackleless lock) on a sturdy, bolted-on hasp. This physically prevents the lid from being lifted without the key or combination. For a cleaner look, some outdoor-rated storage boxes or enclosures come with built-in keyed locks.
For a balance of convenience and security, consider a combination cable lock threaded through the bin's handles or a built-in wheel lock to prevent the entire bin from being rolled away. Remember, the bin itself must be sturdy; a strong lock on a flimsy plastic lid won't help. Ultimately, pairing a robust, animal-resistant bin with a quality padlock offers the most comprehensive security for restricting access to your outdoor trash.