Got ants in your feeder? Make a li'l moat for it with a plastic bottle. Drill a hole in the cap and thread a bolt through it. (I used a 13/64 bit for a 1/4 bolt.) Attach wire hooks, add water. Done.
This was leaking a li'l bit initially, but stopped. You can seal the hole with a washer fashioned from a bit of bike tube (in between the cap and the nut), or hot glue.