Fleece and vet bed are both top layer options. They both wick moisture away buy neither absorb it. So the two together wouldn't really work so well.
Better to use fleece (or vet bed), as the top layer, then an absorbent layer underneath. I have made myself 2 cage liners. The top and bottom layer are fleece, then inside one I have a towel, and inside the other an old mattress protector. I sewed it all together so it'd quick and easy to lay down. You can, however, just lay down a towel or puppy pads or mattress protector (anything absorbent) and then lay a fleece blanket loose on top pf that.
The other option is to buy ready made fleece liners where it's all sewn together for you and ready to use.
The other thing to remember is to wash any new fleece blankets a few times before using them. (5-6 times). If you don't, the urine will just pool on top of the blanket. The washing allows the fleece to start allowing liquid through it which is what you want with a liner.
