We battled cat-door savvy raccoons at the old Shady Rest in Wallingford for years, with considerable success, but the raccoons over here in Ballard are a whole new adversary.
Our electro-magnetic cat door requires a magnet (worn on the cat's collar) as an entry key. The door has a plexiglas flap that swings freely in the outgoing direction as the cat leaves the house but has a magnet-triggered plastic bolt that prevents entry by any animal lacking the key. In Wallingford, the raccoons learned to exploit the weakness in the system (the free-swinging exit) by hooking a claw under the flap, swinging it out and towards them (as if a cat were leaving) and ducking in under the open flap. We foiled them first by changing the control settings so that a second plastic bolt prevented the free-swinging exit. We then installed a second cat door. Under the side-by-side cat doors system, cats used a magnet to enter and to leave, and no doors were free-swinging in any direction.
The Wallingford raccoons responded by ripping the control panel off the second cat door (since it was reversed, the controls were on the exterior), removing the batteries that controlled the lock system, and then ripping the entire cat door assembly out of the door. We fought back by reinstalling the door and covering the controls and the frame of the cat door with one-by-fours screwed into the door itself. Yes, our backdoor in Wallingford looked like something from the set of a made-for-TV tornado disaster film, but we'd won. (I'll spare you the episode that involved the coyote-urine raccoon repellent.)
After realizing we had a nightly visitor here in Ballard, we ordered a second cat door and, while awaiting delivery, locked the current basement cat door so it did not swing out at all, magnet or no magnet. The Ballard raccoon didn't waste any time on skirmishes or vandalism. Sometime during the night, he got a grip on the plexiglas cat door flap and twisted and yanked it until it popped out, right over both plastic locking bolts. This morning I found the flap twisted off-center and jammed in the wide-open position. In the basement, cat food dishes were empty, water bowls muddied, and bags of cat food ravaged.
We've scrapped our plan to reinstitute the "double uni-directional cat door" that worked so well in Wallingford. Mere plastic bolts don't stop Coonzilla. Our fallback plan is to board up the cat door opening for a few weeks and hope the raccoon gives up and moves on easier basements during that time. And, yes, we are going to blockade the door up from the inside so the raccoon can't bring along his little Makita and unscrew the boards.