Coming from a hoarding situation your kitty was probably used to going wherever and whenever he had the need and not being corrected. I would also suggest confining to a bathroom during the day and out at night. Cats are very indifferent to any kind of correcting, like renegaderuby said. If the litter doesn't work, maybe you could try sand? If they stay indoors you don't run the risk of them getting used to going in sand and fowling up a child's sandbox when they are allowed outside.
I'm lucky to have never had a problem with my cats using their litter boxes. Dr.s Foster and Smith has feliway spray. They also have several types of training aids.
As far as aluminum foil goes, it doesn't work for crap. Cats are smarter than aluminum foil. I have a cat that marked everywhere when she was in heat. She would pee on the couch every time she was in heat. Me sitting on the couch didn't stop her she would still pee in between the couch cushions and me if I was in the way. I got the bright idea to put aluminum foil where she was peeing and she just peed on the aluminum foil. She didn't care one bit about it. Although it did make it easier to clean up!