I checked the owl box this morning and it was empty. I flipped the camera on about a half an hour ago and I saw a squirrel - OUCH! I haven't seen a squirrel in the box since I installed the flashing. Apparently the flashing doesn't make the box inaccessible to squirrels, although I'm not sure how the damn squirrel is getting in. Maybe he/she is jumping onto the peaked roof and making access that way? Honestly though, NOTHING in this world will ever be squirrel proof because they are amazing climbers, jumpers etc. In included a YouTube video that illustrates they unbelievable intelligence and athletic ability.
Anyway, the squirrel was poked on prodded with a stick until it made a not so gentle exit out of the front door - making a flying leap to the ground 10 feet below. Will I have more issues with squirrels? No doubt. The nice thing is that I now have the upper hand by having a camera on them 24x7!