That's a great question! A loose dual-bay trash bin is an open invitation to raccoons, stray dogs, and the wind, creating a huge mess. The "best" way to lock it really depends on your specific bin model and what you're trying to keep out.
For a quick and simple fix, heavy-duty bungee cords with hooks are a popular choice. Just stretch one or two across both lids, hooking them onto the bin's handles or lower rim. It's affordable and fast, but determined animals might still pry the lids up a bit.
For stronger security, look at padlocks and hasps. You can install a sturdy hasp (the metal latch) on each lid and use a single padlock through both when closed. This is very effective against pests and casual tampering. Make sure to use weather-resistant hardware.
The most robust solution is a dedicated locking bar or clamp. Many bin manufacturers sell these accessories specifically designed for dual-bay models. They typically involve a metal bar that slides across both lids and locks in place with a key or combination, offering the highest level of security and a clean look.
A key tip regardless of method: always ensure the bin is properly closed and latched before applying any lock. A lock on an unlatched lid is useless! Also, consider your local waste collection rules—some methods might require you to fully unlock the bin on pickup day.
Ultimately, for most homeowners, a combination of the built-in latches plus a sturdy bungee cord or a padlock/hasp setup provides excellent protection without breaking the bank. For high-wildlife areas or commercial use, investing in a manufacturer's locking bar is the best long-term choice.