That's a fantastic and often overlooked question! It gets to the heart of urban design, security, and practical public maintenance. The "most secure" lock isn't a single product but a combination of mechanism, integration, and purpose. For a standard public litter bin, the goal is to deter casual vandalism, scavenging, and misuse while allowing easy, quick access for sanitation crews.
For sheer mechanical toughness, a heavy-duty internal cam lock or a recessed barrel bolt is often the champion. These locks are set into the bin's body, making them hard to pry or smash. Pairing them with a dual-point locking system (locking at two separate latches) significantly increases resistance to forced entry. The key here is minimal external hardware.
However, the landscape is evolving. "Smart" locks with unique electronic keys or codes for authorized personnel are gaining traction. These provide audit trails and eliminate key duplication issues. For high-security areas, bins integrated into fixed street furniture (like a bolted-down bench with a bin) are inherently more secure, as the entire unit must be attacked.
Ultimately, the most secure mechanism is one that is *appropriate*. An impenetrable, complex lock on a park bin is overkill and hinders cleaning. The best systems use robust, hidden mechanical locks made of hardened steel, designed to withstand weather and brute force, while ensuring seamless access for city workers. It's less about a magic lock and more about a well-designed, durable bin where the locking point is just one component of a vandal-resistant whole.