This works on the theory that squirrels are greedy and cannot tread water for very long.
Get a tall Rubbermaid bin. I'm thinking my 18-gallon bin might be too short, so maybe something like a 20-gallon or even a trash can would work. Fill it half way with water and sprinkle some sunflower seeds on the surface. Then lay a piece of wood like a shingle or something across the edge and into the center of the bin with the other end resting on something that the squirrel can walk up to. Maybe if you set it next to some steps or big rocks if you have any. Then sprinkle a few sunflower seeds on the board out to the center of the bin. The board should be somewhat horizontal.
Hopefully the squirrels are not myopic enough that they can see the seeds in the water. One writer reported catching as many as 15 chipmunks in one night with this arrangement.