That's an excellent and very practical question for any restaurant owner or manager. The "most secure" mechanism isn't a single product, but a layered approach tailored to your specific urban challenges—namely deterring theft of grease and valuables, preventing pest access, and stopping unauthorized dumping.
For the highest security, a heavy-duty, shrouded hardened steel padlock (like a disc or puck lock) combined with a steel locking bar or hasp that fully secures both bin lids is the industry standard. The shroud protects the lock cylinder from bolt cutters and weather. This physical barrier is highly effective against opportunistic threats.
For a more integrated solution, consider bins with built-in locking bars that run the width of the container and lock at one or both ends. These are cleaner and harder to tamper with than add-on hasps.
Emerging smart locks with audit trails and access codes offer high-tech control, telling you *who* opened the bin and *when*, which is great for liability management and employee oversight.
Ultimately, your best choice combines a physical deterrent (a quality lock/bar) with operational protocols (strict key control, scheduled put-out times). Start with a premium shrouded padlock on a robust hasp—it's the most reliable and cost-effective first line of defense for the urban restaurant environment.