That's a great question! A slipping liner is one of those small but annoying urban living problems. Over the years, I've tried a bunch of methods, and here are the most effective and simple fixes that actually work.
First, the classic and easiest solution is using binder clips or strong chip bag clips. Simply gather the excess liner at the top of the can and clip it over the rim. For metal cans, strong magnetic clips can also do the trick. It's cheap, immediate, and surprisingly effective.
For a more permanent setup, consider adhesive hooks or velcro strips. Stick a couple of small, sturdy adhesive hooks on the outside of the can, just below the rim. Then, you can hook the bag's "ears" or loops onto them. The 3M Command hooks are great because they remove cleanly if needed.
If your can has handles, bungee cords or elastic bands are lifesavers. Stretch a cord across the top of the can, under the handles, to create a barrier that holds the bag up. You can also criss-cross two cords for extra security on larger cans.
Another clever trick is to create friction. Before putting the liner in, spray a very light mist of water around the inside top of the can. The slight tackiness can help the bag grip the plastic or metal surface and stay in place longer.
Finally, the root cause is often the bag itself. Investing in drawstring bags or bags with reinforced, longer "ears" makes a huge difference. The drawstring can be tied to the can's handles, and the thicker plastic is less likely to tear and slide down.
My personal favorite combo is using a drawstring bag with a couple of small adhesive hooks—it's foolproof. Try a couple of these methods and see which one fits your specific can and routine best. It really does make taking the trash out so much less messy!