Re training litter tray

[Dontgiveamonkeys1350]

My cat is 11. I have had him for a little while now. But he has never used a litter tray here before. I bought one once but he ignored it.
Is there anyway to re train a cat to use a litter tray at this age?

Does he go outdoors?

If he's used to going out, sometimes adding some soil/leaves etc. from the garden can help associate the tray with a place to go.

He does go out. But there are times like at the moment when I could do with him being inside over night. I asked about the heat in a conservatory yesterday. But I think having him in another part of the house over night would be a good idea instead.