You should confine him to a smaller space while he's doing this anyway, it makes the litter tray more accessable for him and easier to retrain him x

as has already been mentioned put him in litter tray after his meals and also at other points too, just to remind him it's there x also scrape his front paw through it so he gets used to the texture of it etc x

The cat attract litter does work, i had to retrain my 4 neuters not to use the garden as the litter tray and it has helped a lot, but not on all of them x

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