No lametta strands. You don't want sparkly Disco Poo in the litter tray.
No precious ornaments made of glass and spun gold costing sixty quid a pop. Although if you spend that on a single ball on a string, you might deserve all you get.
Lights get wrapped around the tree first to avoid dangly bits.
If it's a real tree, cover the surface of the pot. Nobody wants to find out he's got a bit confused and thinks this is now his seasonal toileting arrangements.
Tie the tree down/up/sideways.
If you don't tie the tree down, no fluffy robin or dove shaped decorations. Or jolly mice with Santa hats.
When decorating, have the tinsel in a cat sized box for the Annual Advent Tinsel Cat Photo. You may be allowed to take some of it for the tree if you ask the cat nicely, but don't count on it.
Get children to make decorations. No dangly bits of wool, but lots of brightly coloured card in assorted shapes. Looks good and the cat can't break those. He can also peep out from behind them for photos.
Do not be fooled by him pretending to not be interested. You'll go to bed thinking all is well, only to find chaos in the morning. You've seen the Tom & Jerry Christmas cartoons, haven't you?