This is beginning to get me down, my house stinks and I'm shampooing the carpet daily to try and keep on top of it.
She's blind and old (15) so pretty much sticks to our kitchen/diner, occasional foray into the living room and garden but never goes upstairs.
We first noticed the blindness about 6 months ago, but vet thinks she's gradually lost her sight and it's probably been longer.
She has a litter tray which we always put in the same place it's been kept for the last 10 years and she used for the first few months but lately she's taken to peeing and pooing anywhere and everywhere.
We've taken her back to vet who has done loads of tests and has found nothing wrong, recommended we try leaving a pee-y bit of litter in the tray and one of those plug-in Feliway things. Made no difference
She's not going any more than usual, there's no real pattern to it though. She's never been regular iyswim, and it's never in the same place I can tell when she's about to go, so if I'm in the room and see it I can usually grab her and pop her in her tray before she wees on the floor/sofa/whatever.
The litter tray is one we've been using for a while and we've been using the same litter for years. She's still quite sprightly so I don't think there's a problem getting in it, she can still jump up onto the sofa or dining chairs, climbs up the fence, etc.
It's like she can't really be bothered to find her tray iyswim, we leave some dirty litter in it and always leave it in the same place so she should be able to find it easily enough - she finds her food bowls no problems