My cats roughly 18-24 months old, for his first year he was kept indoors at all times,he had no problems using the litter tray and was fantastic. Then we started letting him outside eventually we left the little toilet windows open so he could come in and out of the house as he pleased during the day but brought him in at night, and outside we left another litter tray under a little shelter and this worked great but for the past 2-3 months, he first stopped using the outside litter tray doing his business at the bottom of the garden, then a few weeks later he has stopped using the in door tray also and thats where we are at now. He is not doing it about the house (yet) but fear he might start. Anyone any advice on this?