Well, not being as persistant as you I just gave up on feeding the little fellers becuase my squirels got promoted to RATS, at that point I just ceased feeding. The main ALPHA rat got so large and cocky he didn't even bother to do a runner till I was almost within arms reach. He did get very very fat tho, and one night last fall, it was dusk and I had not turned any lights on yet and my little doggie friend brought something in the house, which was of a similar size to himself (he's a Shi Tzu) and when I switched on a light it was Mr Ratty, Mr VERY BIG FAT RATTY..
Bird feeding ceased there and then.
I may now try your fail safe method, I shall be sueing you if it doesn't work, or, if Mr Ratty mark 2 comes a calling.
Thanks
Asa