That's a great question, and a common challenge for property managers and municipalities. The "best" lock really depends on your specific needs, but for most public outdoor trash cans or dumpsters, the goal is to deter casual tampering, unauthorized dumping, and animal access without making legitimate waste collection a hassle.
For standalone dumpsters or enclosures with a hasp, a heavy-duty shackleless padlock or a heavy-duty combination padlock is often the top choice. Shackleless models are excellent because the lock body sits inside the hasp, making it extremely difficult to cut with bolt cutters. Combination locks eliminate the issue of lost keys when multiple custodial staff need access.
For cans with flip lids, consider integrated lid locks or cable locks. These secure the lid to the handle or a fixed point, preventing it from being fully opened. For a whole enclosure gate, a weather-resistant padlock paired with a robust hasp that's welded or through-bolted (not just screwed on) is essential.
The key is balancing security with practicality. You want a lock strong enough to be a deterrent, but one that authorized personnel can open reliably. For high-traffic public areas, a combination or key-alike system (where many locks use the same key) often works best. Always prioritize solid, welded-on hardware; a strong lock on a weak hasp is pointless.