fouling cats

i have a 19 year old female cat who does not care where she goes to the toilet. we provide a litter tray which is kept clean. but she will dissapear upstairs and use the carpet as a loo. im at my wits end. any ideas?

Is this a new behavior?
   
She may be having problems getting into and out of the box at her age.
   
Try a lower box and see if that helps.
   
Also, when they get as old as she is, sometimes they get prissy and no longer like the feel of litter on their paws so try changing to a more natural litter and see if she prefers it.
   
If she has a special spot on the carpet where she is going, put the litter box there to remind her that this is where she is supposed to go.
   
If none of this works and she is still consistently going on the one spot on the carpet, at her age I guess you have to suck it up and put down wee wee pads for her in that spot and pray that she will be courteous enough to use them.
   
If all else fails, break out the nappies.
   
If she cannot be trusted indoors, then she wears the diaper. Remove it when she goes outside but the minute her paws are indoors, back on her it goes.
   
Sometimes the diaper gets them back on track. Put it on her then let her wet herself and leave the wet diaper on her (if she is pooping indoors then let her poop the diaper as well).
   
Leave it on her for a good half hour so she can get a good dose of the misery of wearing a soiled one, then change her.
   
If you change her the moment she soils then she will be comfortable and will have no problem wetting and pooping her pants since you will be right there to clean her bum.
   
You might find her crying at the door to go outside to potty.
   
If she starts to consistently keep her diapers clean you can try going without but the moment she wets the carpet, back on they go.
   
Your worst case scenario is that she spends the rest of her life in diapers but at her age that isn't likely to be a huge period of time and it is easier to change her and toss her dirty diapers than it is to constantly clean the carpet.
   
Good luck, hope something works out here.