My 15-year-old senior cat is getting sloppy about making sure she is urinating inside the litter box. There's no evidence of breaking litterbox protocol otherwise, so I don't think she's indicating illness or annoyance (other than possible early senility), though I'll have the vet look at her. She seems to just be just getting careless.
This is usually OK since it's a covered box and the sides catch it, and I've taken to putting "pee pads" in front of the door so mistakes get caught. Not a big deal.
If I catch her I can tap her gently and she'll be startled into stopping, but I don't want her to think the box is wrong generally, and I'd rather not have to follow her to make sure I'm there to do so.
So I'm wondering whether anyone has had success retraining an older cat on where the sides of the box are, and whether there's a recommended approach to doing so, short of going all the way back to kitten-training.