I've put these pictures up before, but the title under which it was posted would be misleading, so here they are again.
This is a 4 foot length of 4" dia ABS pipe from Lowes, who sell the stuff conveniently pre-cut to length. The bucket is a household cleaning bucket, filled with water. The pipe is secured to the fence with a small bungee cord so it won't tip over.
You bait this thing by smearing some peanut butter, first a bit on the top of the pipe, and a bit more elbow deep down the pipe from the top. Squirrels can smell peanut butter from blocks away. They sample the stuff on top, then try to get the stuff down the pipe, which is a bit out of reach for a squirrel hanging by its hind legs from the rim of the pipe.
Splish splash, they'll be takin' a bath, and drown in fairly short order. Disposal is up to you, but in my neighborhood, there is a family of foxes who will carry away any freshly dead small animals overnight.
For you Terry Pratchett fans, this is a lot like being a devotee of Offler, the crocodile god. You have a small statue of Offler in your house, in front of which you leave a small offering of meat at night. In the morning the meat is gone, and your life is relieved of minor inconveniences.
If you're the kindly type, I suppose you could modify a wire frame cage to accept the pipe, and add a barrier to close when you withdraw the pipe. The little varmints can then be relocated to a new home, which I suggest should be at least 5 miles away. Select and modify your cage carefully, because the first time an insanely angry, panic-stricken squirrel breaks jail in your car, the novelty of being the cheauffer is going to wear off mighty quickly.